[Rust/UTXO/Bitcoin] Finalize Bitcoin V2 implementation in Rust (_updated_)

[lamafab]

Work-in-Progress: More docs to follow

[lamafab]

Final update, I'm no longer going to be working on this:

Summarized task list of what has been completed and was is still open, not including finer details, edge cases and tests.

tw_keypair:

• Support for Schnorr signatures
• Optional cleanups/improvements (see TODOs)

tw_utxo:

• Address generation and derivation for Legacy, Segwit and Taproot.
• Script builders for inputs and outputs (claiming and spending conditions):
  • Legacy such as P2SH, P2PH and P2PKH
  • Segwit such as P2WSH and P2WPKH
  • Taproot such as P2TR key-path (transfers) and P2TR script-path (complex)
• Builder APIs:
  • Transaction construction and Sighash calculation
    • TXID calculation (!!)
  • Fee estimation and final calculation
  • BRC20 construction
  • Ordinal construction
• UTXO input selection

tw_bitcoin:

• Mapping proto structures to tw_utxo builders for inputs and outputs.
  • Done for most expect p2wsh and ordinal_inscribe
    • (see brc20_inscribe for reference)
• Migrate entry.rs to new tw_utxo interfaces.
  • Migrate preimage_impl
  • Migrate compile_impl
    • (largely done but still needs some cleanups)

General:

• Update, improve and/or deprecate any existing tests.