[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:

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

tw_utxo:

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

tw_bitcoin:

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

General:

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