bark, bark-rest: Deterministic exit fee estimation

Peterrequested to merge
exit-estimate-arithmetic into master
  • check or remove this line after you've added a CHANGELOG entry or if your PR doesn't need one (they should go into CHANGELOG/unreleased/)

Reworks estimate_emergency_exit_fee from a wallet-simulated CPFP walk into weight arithmetic: each pending package is priced at the requested rate with a canonical child (the same MakeCpfpFees::package_fee rule the real CPFP builder uses), scaled by a caller-supplied fee_margin (default 1.2). The estimate no longer touches the on-chain wallet, so it works with any wallet, and an invalid margin is a typed error rather than a panic.

Also extracts the collection of unconfirmed exit transactions into a shared ChildState-based collector (used by the follow-up presign and remaining-transactions MRs), which now rejects VTXOs spent outside the exit flow and no longer bumps packages already paying the requested rate.

Merge request reports