Complete PSBT Workflow Implementation Including Multisig Support and Script Enhancements

[JAGADISHSUNILPEDNEKAR]

This pull request introduces a complete suite of Python scripts that collectively implement an end-to-end Partially Signed Bitcoin Transaction (PSBT) workflow using a 2-of-3 multisig setup on Bitcoin Testnet. The contributions include:

Key Additions:

1. create_psbt_multisig.py

   • Generates a 2-of-3 P2WSH multisig address.
   • Creates an unsigned transaction using real testnet UTXOs.
   • Produces a base64-encoded PSBT ready for signing.

2. sign_psbt.py

   • Allows signing of a specific PSBT input using a private key in WIF format.
   • Supports custom sighash types.

3. combine_psbt.py

   • Combines multiple partially signed PSBTs into a single PSBT.

4. finalize_psbt.py

   • Finalizes a PSBT and optionally validates the resulting transaction.
   • Prints hex-encoded signed transaction ready for broadcast.

5. psbt.py

   • Core implementation of the PSBT class
   • Logic for signing, combining, finalizing, and analyzing PSBT contents.

6. Modified Script Class

   • Extended Script class to enhance parsing, formatting, and identification of script types (e.g., P2WPKH, P2WSH, multisig).
   • Provides serialization, deserialization, and address generation from witness scripts.