Add a simple test that uses how to modify the swap-in-potentiam protocol to use musig2 and taproot:
- taproot key path is used for the mutual user key + server key use case, which sends to a single musig2 aggregated key
- tapscript path is used for the refund case (user key + delay)

Add another example with taproot but not musig2 that uses 2 differents scripts (mutual case and refund case)

This message includes all outputs from the remote tx and not just the one that is included in the swap.
This is needed for Schnorr signatures.

This allows us to easily rotate swap-in addresses and generate a single generic taproot descriptor (for bitcoin core 26 and newer) that can be used to recover
swap-in funds once the refund delay has passed, assuming that:
- user and server keys are static
- user refund keys follow BIP derivation

It makes the code cleaner and we get rid of the secret nonces map.
These nonces are replaced with dummy values whenever this classes are serialized, which is safe since they're never reused for signing txs.

Instead of sending an explicit serialId -> nonce map, we send a list of public nonces ordered by serial id.
This matches how signatures are sent in TxSignatures.