[PoC/Bitcoin/Utxo] Correctly Consider Fees for UTXO Selection

[lamafab]

See #3666 for more context.

Update

So, I know made the following changes:

• The input selector in tw_utxo now considers fees in UTXO selection.
• Implement a bunch of extra sanity checks internally.
• Correctly update selected UTXOs returned by tw_utxo when calling it indirectly via BitcoinEntry.sign.
• The InputSelector::SelectAscending is used by default.
• Simplify the transaction builder; Brc20Plan now returns the signed outputs directly (@JaimeToca ).
• Add new test module input_selection.rs which checks the input selection and fee calculation accordingly.
  • Remove weight/fee checks in tw_utxo, I need to adjust/inspect those later (covered in input_selection.rs).
  • Remove fee_estimate.rs, covered in input_selection.rs
  • Remove the BitcoinPlanBuilder (for now).

Overall this is good to go, but I'd like to take some extra time for the polishing. @JaimeToca could already make use of this, so I can push the polishing in another PR.

[satoshiotomakan]

The estimation algorithm looks promising and quite clear to understand!
I have only one major change request, please consider it t be changed or discussed