ToPrivateString() behaviour will be modified in the following commits.
This change ensures that wallet migration does not break.

- Refactor Descriptor::ToPrivateString() to allow descriptors with missing private keys to printed. Useful in descriptors with multiple keys e.g tr() etc.
- The existing behaviour of listdescriptors is preserved as much as possible, if no private keys are availablle ToPrivateString will return false

unused() descriptors do not have scriptPubKeys. Instead, the wallet uses
them to store keys without having any scripts to watch for.

A helper method to obtain all unused(key) descriptor SPKMs.

When a wallet contains only an unused(KEY) descriptor, use it. Previously the user would have to call listdescriptors and manually specify it.

There will be other functions within MutableTransactionSignatureCreator
that need to compute the same sighash, so make it a separate member
function.

Adds GetMuSig2SecNonces which returns secp256k1_musig_secnonce*, and
DeleteMuSig2Session which removes the MuSig2 secnonce from wherever it
was retrieved. FlatSigningProvider stores it as a pointer to a map of
session id to secnonce so that deletion will actually delete from the
object that actually owns the secnonces.

The session id is just a unique identifier for the caller to determine
what secnonces have been created.

Expand taproot tests to cover avoid_script_path in  walletprocesspsbt.

When avoiding script paths, there's no need for the workaround that increases fee_rate to compensate for the wallet's inability to estimate fees for script path spends. We use this to indirectly test that key path was used.

We also check that taproot_script_path_sigs is not set.

Finally, for transactions that can't be signed using their key path, we try again by allowing the script path.

Additional test extended private keys were extracted from other tests.

Conflicts:
	src/script/sign.cpp

Using m_options.sighash_type

Conflicts:
	src/wallet/external_signer_scriptpubkeyman.h
	src/wallet/rpc/wallet.cpp

An earlier merge commit contained an outdated version of this.

…ys' into 2025/06/musig2-power

External signer enabled wallets should always use the process PSBT flow.
Avoid going through CreateTransaction.

This has no effect until the next commit when WALLET_FLAG_EXTERNAL_SIGNER
no longer implies WALLET_FLAG_DISABLE_PRIVATE_KEYS. Without this change
signing with the GUI would break for external signers with private keys
enabled.

Also document it and take a reference.

BIP 379 allows height and time locks that have no consensus meaning in BIP 68 / BIP 112.
This is used by some protocols like Lightning to encode extra data, but is unsafe when
used unintentionally. E.g. older(65536) is equivalent to older(1).

This commit prevents accidental import of such descriptors. They will be rejected unless
marked 'unsafe' in importdescriptors.

Wallets that already contain such a descriptor are not impacted.