feat(wasm-utxo): add sighash support to MuSig2 partial signatures

Support sighash type in MuSig2 partial signatures by appending the sighash
byte to the 32-byte signature when not using the default sighash type.
Adds helper functions to get and manage sighash types consistently
throughout the signing process.

Issue: BTC-2669

Co-authored-by: llm-git <llm-git@ttll.de>

Author: OttoAllmendinger