Add PSBT (Partially Signed Bitcoin Transaction) Support - BIP 174

[JAGADISHSUNILPEDNEKAR]

Add PSBT (BIP-174) Support

Overview

This PR implements Partially Signed Bitcoin Transaction (PSBT) functionality as defined in BIP-174. After careful study of the specification, I've created a focused implementation that integrates with the existing codebase while maintaining its structure and style.

Changes

• Added core PSBT implementation in bitcoinutils/psbt.py
• Created five example files demonstrating PSBT usage:
  • create_psbt.py: Creating new PSBTs
  • sign_psbt.py: Signing inputs with private keys
  • combine_psbt.py: Combining partially signed PSBTs
  • finalize_psbt.py: Finalizing PSBTs for broadcast
  • psbt_multisig_wallet.py: Using PSBTs with multisig wallets
• Added four targeted test files following existing patterns:
  • test_psbt.py: Core PSBT creation and parsing
  • test_psbt_sign.py: PSBT signing functionality
  • test_psbt_combine.py: Combining multiple PSBTs
  • test_psbt_finalize.py: Finalizing and extracting transactions

Implementation Notes

• All functionality follows BIP-174 specification
• Made minimal changes to existing files
• Tests use the current testing framework with no additional dependencies
• Each component is thoroughly tested and documented

Testing

All tests are passing

This PR focuses exclusively on PSBT functionality without introducing unrelated changes or dependencies.

[JAGADISHSUNILPEDNEKAR]

Hi @karask
Last time,I had not implemented the things which you mentioned. I am extremely sorry that I disappointed you with my work but this time I took your feedback to my heart and have hopefully made all the changes which you had asked me to implement

I would highly love to listen to your feedback on this PR
Let me know if you need any further changes in this
I would try to implement this asap!!

[JAGADISHSUNILPEDNEKAR]

All the tests are passing

[JAGADISHSUNILPEDNEKAR]

Only the necessary files related to PSBT implementation are present
Kept the codebase clean

[karask]

Hi @JAGADISHSUNILPEDNEKAR I will not check PSBT code (from anyone) anymore, until the proposals come in. In the proposals I expect to see the design, rationale, how you intend to implement it, etc.

[JAGADISHSUNILPEDNEKAR]

Okay I will keep this in mind and work on some other issues
I have already started to implement some TODOs
Would love your feedback :)

[karask]

Closing since we are working on the design / implementation from scratch.