ce7d94a doc: add release note (Sjors Provoost)
71f29d4 doc: update build and dependencies docs for IPC (Sjors Provoost)
3cbf747 cmake: set ENABLE_IPC by default (Sjors Provoost)
32a90e1 ci: use bitcoin-node for one depends job (Sjors Provoost)
b333cc1 ci: build one depends job without multiprocess (Sjors Provoost)
16bce9a build: depends makes libmultiprocess by default (Sjors Provoost)

Pull request description:

  Have depends make libmultiprocess by default. This PR causes the following behavior changes:

  1. **bitcoin-node and bitcoin-gui binaries are included in releases**, due to `ENABLE_IPC` option being switched on by default in depends builds
  2. `ENABLE_IPC` is also switched on by default in non-depends builds (instructions updated, #33190 does this as a standalone PR)
  3. Various changes to CI: switching on `ENABLE_IPC` on in most configurations and using `bitcoin-node` binary (`bitcoin -m`) for functional tests in two of them.
  4. The `bitcoin-node` and `bitcoin-gui` are added to `Maintenance.cmake` (since they're now in the release)

  This PR doesn't need to do all of these things at once. However it's is simpler, avoids code churn (especially in CI), and  probably less confusing to make all these changes in the same PR.

  Windows is not supported yet, so `ENABLE_IPC` is off by default for it. It can be enabled after #32387.

  The initial main use case for IPC is to enable experimental support for the Mining IPC interface. A working example of a Stratum v2 Template Provider client using this interface can be found here: Sjors#48.

  See #31756 for discussion of when this should happen. Supersedes #30975.

  ## Wait what, why?

  The [Stratum v2 spec](https://stratumprotocol.org/specification) has been around for a few years now, mostly stable but with [ongoing activity](https://github.com/stratum-mining/sv2-spec/commits/main/) to clarify and fix more subtle issues encountered by implementers. Most of the implementation is built in Rust in a project called the Stratum Reference Implementation ([SRI](https://github.com/stratum-mining/stratum)).

  [Braiins](https://demand.work) added Stratum v2 support to both their (custom) firmware and pool several years ago, though they have fallen behind on recent spec changes (update: it seems they've fixed that). Apparently [new hardware is underway](#31802 (comment)) that supports Stratum v2 without the need for custom firmware.

  [DMND pool](https://www.dmnd.work) is Stratum v2 native from the start and employs several of the SRI developers (they haven't fully launched though). The industry is rather secretive, but apparently [there is more underway](#31802 (comment)).

  What does Bitcoin Core have to do with this? Well, in Stratum v2 jargon we are the Template Provider.

  Or at least, the Template Provider role needs us to make block templates. Initially back in 2023 the plan was to have Bitcoin Core implement this role entirely, see #23049. It would speak the sv2 encrypted message protocol. In fact the spec was designed around this assumption, making sure to only use cryptographic primitives already in our codebase.

  I took over that effort in late 2023, but during 2024 it became quite clear there was [strong resistance](#29432 (review)) to the idea of including all this new code, opening another network ports, etc.

  At the same time there was the long running multiprocess / IPC project #10102, and the idea was born to apply that here: instead of including Stratum v2 specific stuff, we offer a general Mining interface via an IPC connection that can e.g. push out fresh block templates as fees rise above a threshold (something not possible and/or very inefficient with `getblocktemplate`). A client sidecar application then sits between the Stratum v2 world and our node.

  Currently there's only one such sidecar application, maintained by me, and reusing the same codebase from the integrated approach. An attempt has been made to connect to our interface from Rust bitcoin-core/libmultiprocess#174, which would pave the way for SRI include the Template Provider role. Plebhash below indicates he's also working on that: #31802 (comment).

  So with this new approach in mind, between mid 2024 until spring 2025, I introduced a new Mining interface (#30200 - #31785). At the same time Russ Ryanosky worked on more tight integration of [libmultiprocess](https://github.com/bitcoin-core/libmultiprocess), including making it a subtree in #31741. See [design/multiprocess.md](https://github.com/bitcoin/bitcoin/blob/master/doc/design/multiprocess.md).

  Meanwhile I've been maintaining a fork of Bitcoin Core that includes the Template Provider, in the original integrated approach (Sjors#68) as well as an IPC + sidecar variant (Sjors#48). I've been shipping [regular releases](https://github.com/Sjors/bitcoin/releases), mostly after bug fixes or major rebases. The SRI team has been testing both variants, though the "official" [instruction on their web page](https://stratumprotocol.org/developers) is to stick to integrated version. Bug reports on [my repo fork](https://github.com/Sjors/bitcoin/issues?q=is%3Aissue) as well as on the [SRI repo](https://github.com/stratum-mining/stratum/issues?q=is%3Aissue%20%20label%3A%22template%20provider%22) are evidence of actual testing happening.

  But as Pavlenex writes below:

  > one recurring feedback I kept getting regardless of the size/type of miner is that the need to run a forked version of Bitcoin Core remains a significant barrier to adoption

  This PR gets rids of that significant barrier. People can download a "pristine" version of Bitcoin Core and the only change is to start it with `bitcoin node -m -ipcconnect=unix` instead of the usual `bitcoind`.

  Once that's released, I can dramatically simplify my sidecar codebase (Sjors#48) by removing pretty much all Bitcoin Core code  that it doesn't need. My plan is to then make that a separate repository, which should be much easier to contribute to. I can then also make (deterministically built) signed releases, while making it clear that sidecar code has nothing to do with Bitcoin Core. Perhaps later on SRI implements the same and I can stop maintaining that project.

  Conceptually the situation will be a lot clearer;
  - today: download forked version of `bitcoind` (or a forked version of `bitcoin-node`, plus `bitcoin-mine`), install SRI stuff
  - tomorrow: download Bitcoin Core v30, install `bitcoin-mine` and SRI
  - future: download Bitcoin Core v30 and SRI

  <details>
  <summary>
  Guix hashes:
  </summary>

  ```
  find guix-build-$(git rev-parse --short=12 HEAD)/output/ -type f -print0 | env LC_ALL=C sort -z | xargs -r0 sha256sum
  6dbf29baecb1d1593087ef1306ae7c78aa160c8beb04dc016e02549ae2d6d90d  guix-build-ce7d94a492e6/output/aarch64-linux-gnu/SHA256SUMS.part
  4b465e5e8f9652c176aa57cfe5c289267c28c3a3c684034a9ce471b529b95275  guix-build-ce7d94a492e6/output/aarch64-linux-gnu/bitcoin-ce7d94a492e6-aarch64-linux-gnu-debug.tar.gz
  85bc6fa008b83419d96443d9dcc212b46f0992387fd58fd2dda5da76536ee22c  guix-build-ce7d94a492e6/output/aarch64-linux-gnu/bitcoin-ce7d94a492e6-aarch64-linux-gnu.tar.gz
  5ed9ea52a8bd55361d2d9c01fbd1b25ec9970530c2776e6c1959424ba1689f52  guix-build-ce7d94a492e6/output/arm-linux-gnueabihf/SHA256SUMS.part
  2e483011fac64462d3aa000b577c3c05c825506032d879e39612e096d7a6c65b  guix-build-ce7d94a492e6/output/arm-linux-gnueabihf/bitcoin-ce7d94a492e6-arm-linux-gnueabihf-debug.tar.gz
  7ff1e3ba54944a2be89dd7d68cb91dff6f8950de9d7b521e15dfb746965f81bd  guix-build-ce7d94a492e6/output/arm-linux-gnueabihf/bitcoin-ce7d94a492e6-arm-linux-gnueabihf.tar.gz
  abdf89e701b21b8c1238a8cec46aeaa55e0c3a0b88ad718636e89cde9813ca08  guix-build-ce7d94a492e6/output/arm64-apple-darwin/SHA256SUMS.part
  fb55cff0296cd5474811fe5cedcf28603628729dd085eeefa007c72582459b33  guix-build-ce7d94a492e6/output/arm64-apple-darwin/bitcoin-ce7d94a492e6-arm64-apple-darwin-codesigning.tar.gz
  e9aa566b1e79c467d7987b7c68fa608db788e6ddf89c4d90e524cd47b4faaf86  guix-build-ce7d94a492e6/output/arm64-apple-darwin/bitcoin-ce7d94a492e6-arm64-apple-darwin-unsigned.tar.gz
  bb428fc62a1230a55f49fa3b5c7ba8d588e8fed491357f890d5a6724a38b14e9  guix-build-ce7d94a492e6/output/arm64-apple-darwin/bitcoin-ce7d94a492e6-arm64-apple-darwin-unsigned.zip
  5ef4b75e94b2c8265fbc588bbb42467a84438af969fddac0ea61ced3e4113345  guix-build-ce7d94a492e6/output/dist-archive/bitcoin-ce7d94a492e6.tar.gz
  4f55d56a108c8f312a502cd5dfdf0840b091861a6d502df31caf4636a203697a  guix-build-ce7d94a492e6/output/powerpc64-linux-gnu/SHA256SUMS.part
  66c5b1242c60e37098885a00e24efe19baee4afcd2e3d6407207523d8872f055  guix-build-ce7d94a492e6/output/powerpc64-linux-gnu/bitcoin-ce7d94a492e6-powerpc64-linux-gnu-debug.tar.gz
  d9dbbee7217544eda26e77158cd82caeaef2b40fb9fc7033323e7ffe64264109  guix-build-ce7d94a492e6/output/powerpc64-linux-gnu/bitcoin-ce7d94a492e6-powerpc64-linux-gnu.tar.gz
  d9b808cc5685c819abcebb4ace65f003ebc4bfedf3fca046b34de37994358782  guix-build-ce7d94a492e6/output/riscv64-linux-gnu/SHA256SUMS.part
  eeeea470b1cf76515bfae14c779a3ea356d89f719d1fef1a81e8f0d6b04ab747  guix-build-ce7d94a492e6/output/riscv64-linux-gnu/bitcoin-ce7d94a492e6-riscv64-linux-gnu-debug.tar.gz
  9993da4eb51618b8bd25ec88cc576496720e5589315e9eba6f3ddab25f9c3e60  guix-build-ce7d94a492e6/output/riscv64-linux-gnu/bitcoin-ce7d94a492e6-riscv64-linux-gnu.tar.gz
  1b5a676580e0e79598d182f6ebbb05fb8aee2381edc3c09c042cae2600f448ab  guix-build-ce7d94a492e6/output/x86_64-apple-darwin/SHA256SUMS.part
  9152122d95a34d5df75305c6883c87707e7b09033fffd08e264d703ed177ef12  guix-build-ce7d94a492e6/output/x86_64-apple-darwin/bitcoin-ce7d94a492e6-x86_64-apple-darwin-codesigning.tar.gz
  2793f75730dbef6bdf12b5ed7135e22ed21178abff2926dee92843837d4ab544  guix-build-ce7d94a492e6/output/x86_64-apple-darwin/bitcoin-ce7d94a492e6-x86_64-apple-darwin-unsigned.tar.gz
  e89aafd7e4a330a41f470e8f0a91ea876fad7d19547b404600867413f1a8ccb7  guix-build-ce7d94a492e6/output/x86_64-apple-darwin/bitcoin-ce7d94a492e6-x86_64-apple-darwin-unsigned.zip
  955b27f881927a86da3c566357ad8ca68dbe17e9652bde8c482a57ceacba92cb  guix-build-ce7d94a492e6/output/x86_64-linux-gnu/SHA256SUMS.part
  fd012be97bdf5c75ac12ddef21526bfdb5e17ecc77cde9c34d832194b0dc3293  guix-build-ce7d94a492e6/output/x86_64-linux-gnu/bitcoin-ce7d94a492e6-x86_64-linux-gnu-debug.tar.gz
  0ecf7f80e9049369760d0e27fe6c026391ab25eae0f42336bef43e51a2621726  guix-build-ce7d94a492e6/output/x86_64-linux-gnu/bitcoin-ce7d94a492e6-x86_64-linux-gnu.tar.gz
  2e8085f5fecc246d841b0bf6f28ecd0684a6cee49252fc88c1019d7586c7b7a2  guix-build-ce7d94a492e6/output/x86_64-w64-mingw32/SHA256SUMS.part
  c60041e8137eda352557254c5f67fb83eeb97ecfec342ee528451bd44ee4523a  guix-build-ce7d94a492e6/output/x86_64-w64-mingw32/bitcoin-ce7d94a492e6-win64-codesigning.tar.gz
  b1be6b2f4de1c69c2e0e4de6dd97a4891ae9eb50d89435ef47247b5a187915a9  guix-build-ce7d94a492e6/output/x86_64-w64-mingw32/bitcoin-ce7d94a492e6-win64-debug.zip
  bfe143f41a20c537145c7044aca889b28efe19072b0150042a3bd865983b3d7e  guix-build-ce7d94a492e6/output/x86_64-w64-mingw32/bitcoin-ce7d94a492e6-win64-setup-unsigned.exe
  94a906b83d84db7b25f7e3cfdce2a2030243f2ee6cc70b1fc088459f0b2f382d  guix-build-ce7d94a492e6/output/x86_64-w64-mingw32/bitcoin-ce7d94a492e6-win64-unsigned.zip
  ```

  </details>

ACKs for top commit:
  ryanofsky:
    Code review ACK ce7d94a. This was just rebased to fix a conflict since last review.
  josibake:
    ACK ce7d94a
  achow101:
    ACK ce7d94a
  ismaelsadeeq:
    ACK ce7d94a and tested again on macOS by building via depends and source.
  janb84:
    ACK ce7d94a

Tree-SHA512: f7ab72933854e9dfce5746cdf764944bc26eec815f97cd0aa6b54fa499c3cccb1b678861ef5c1c793de28153d46bbb6e4d1b9aa0652163b74262e2d55ec8b813