c0045e6cee Add test for multipath miniscript expression (David Gumberg)
b4ac48090f descriptor: Use InferXOnlyPubkey for miniscript XOnly pubkey from script (Ava Chow)
4c50c21f6b tests: Check ExpandPrivate matches for both parsed descriptors (Ava Chow)
092569e858 descriptor: Try the other parity in ConstPubkeyProvider::GetPrivKey() (Ava Chow)
Pull request description:
When a `ConstPubkeyProvider` is xonly, the stored pubkey does not necessarily have the correct parity bit. `ToPrivateString()` is correctly handling this by looking up the keys for both parity bits, but `GetPrivKey` does not. This results in not finding the private key when it is actually available if its pubkey has the other parity bit value.
To fix this, this key finding is refactored into `GetPrivKey()` so that its behavior is corrected, and `ToPrivateString()` is changed to use `GetPrivKey()` as well.
Additionally, the descriptor test checks are updated to include a check for `ExpandPrivate()` to verify that both the parsed public and private descriptors produce `SigningProvider`s with the same contents.
Fixes#31589
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