Add PSBT creator, signer and finalizer roles for BIP-322

[aagbotemi]

Summary

Implement BIP-322's multi-party PSBT workflow, a creator builds an unsigned signing request, independent signers add partial signatures after detecting the request, and a finalizer assembles and encodes the result.

Rebased on #73

Changes

• Add detect_bip322_psbt to check the detection properties.
• Add Bip322Psbt to carry the detected message and challenge for signers.
• Add create_bip322_psbt to build an unsigned PSBT with the message, UTXO, and script fields set.
• Add sign_bip322_psbt_input to detect the request, adds a partial signature (or tap_key_sig for taproot) to the first input.
• Add finalize_bip322_psbt to assemble signatures per BIP174 and encodes as a ful signature.
• Split create_to_spend into a script-based create_to_spend_from_script so detection can reconstruct to_spend from a scriptPubKey.

Closes #74