Implement BIP-174 PSBT Support

[Shahil3]

The following features are included:
•PSBT parsing from hex and serialization back to hex
•Validation of global, input, and output maps using BIP-174 rules
•Input type detection (e.g., P2PKH, P2WSH, P2SH-P2WPKH)
•UTXO field validation: non-witness and witness handling
•Partial signature parsing and completeness check (for multisig)
•Input finalization (scriptSig and witness stack)
• Full transaction extraction if all inputs are finalized

[karask]

Hi @Shahil3 and thank you for the contribution.

Please make the test similar to all the other tests. Also please include some examples to demonstrate the usage of PSBT.

I will then review the code.

[defconradio]

python3 tt.py 
==== PSBT Robust Test ====

1. Testing PSBT parsing from hex...
Traceback (most recent call last):
  File "/home/analiser/Someone-s-There/python-bitcoin-utils/tt.py", line 119, in <module>
    run_tests()
  File "/home/analiser/Someone-s-There/python-bitcoin-utils/tt.py", line 15, in run_tests
    psbt = PSBT.from_hex(psbt_hex)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/analiser/Someone-s-There/python-bitcoin-utils/bitcoinutils/psbt.py", line 295, in from_hex
    return cls.from_bytes(binascii.unhexlify(hex_string))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/analiser/Someone-s-There/python-bitcoin-utils/bitcoinutils/psbt.py", line 354, in from_bytes
    raise ValueError(f"Input #{idx} in unsigned tx already contains a scriptSig")
ValueError: Input #0 in unsigned tx already contains a scriptSig

[karask]

Proposals have finished and another PSBT design / implementation was selected. Thank you for working on this!