ead4468 cmake: Use `HINTS` instead of `PATHS` in `find_*` commands (Hennadii Stepanov)

Pull request description:

  According to the CMake documentation, `HINTS` "should be paths computed by system introspection, such as a hint provided by the location of another item already found", which is precisely the case in the `FindQRencode` module.

  Entries in `HINTS` are searched before those in `PATHS`. On macOS, Homebrew’s `libqrencode` will therefore be located at its real path rather than via the symlink in the default prefix.

  A backport to 29.x is required for #32804, as this change prevents contamination of include directories by broad locations such as `/usr/local/include` or `/opt/homebrew/include`, which take precedence over Qt’s `-iframework` flags.

  Below is the relevant change in the configuration logs on my macOS 15.5 `x64`:
  - master branch @ ead4468:
  ```
  % cmake -B build -DBUILD_GUI=ON
  <snip>
  -- Found QRencode: /usr/local/lib/libqrencode.dylib (found version "4.1.1")
  <snip>
  ```
  - this PR:
  ```
  % cmake -B build -DBUILD_GUI=ON
  <snip>
  -- Found QRencode: /usr/local/Cellar/qrencode/4.1.1/lib/libqrencode.dylib (found version "4.1.1")
  <snip>
  ```

ACKs for top commit:
  fanquake:
    ACK ead4468

Tree-SHA512: 1f0b04e3efeb7fe3efbb969be911abbcf56030d715acd87c0fbaf24422cdf1122f169e32242571256916c96a159212842e1e73092145c63ecc495ce429c6e587

…ackage

8800b5a cmake: Explicitly specify `Boost_ROOT` for Homebrew's package (Hennadii Stepanov)

Pull request description:

  On macOS, this PR ensures that the Boost package is located at its real path rather than via the symlink in the default prefix.

  A backport to 29.x is required for #32804, as this change prevents contamination of include directories by broad locations such as `/usr/local/include` or `/opt/homebrew/include`, which take precedence over Qt’s `-iframework` flags.

  Below is the relevant change in the configuration logs on my macOS 15.5 `x64`:
  - master branch @ ead4468:
  ```
  % cmake -B build
  <snip>
  -- Found Boost: /usr/local/include (found suitable version "1.88.0", minimum required is "1.73.0")
  <snip>
  ```
  - this PR:
  ```
  % cmake -B build
  <snip>
  -- Found Boost: /usr/local/opt/boost/include (found suitable version "1.88.0", minimum required is "1.73.0")
  <snip>
  ```

  This PR is forward-compatible with the changes proposed in #32667.

ACKs for top commit:
  fanquake:
    ACK 8800b5a Checked that this plus #32805 fixes #31009

Tree-SHA512: 114bd945ec0c06a8d15b565e5b9aafc3bcfdf2a4ba4400e072b8e31053dff0f9ef423b941ee1dff2113f83e08f7fada728383ae88b3ec380b5c3e40553205f7d