chore(tests): replace deprecated FeeRate::from_sat_per_vb_unchecked

[none34829]

Description

bitcoin-units 0.1.3 deprecated FeeRate::from_sat_per_vb_unchecked in favor of FeeRate::from_sat_per_vb_u32. Cargo resolves any 0.1.x automatically, so fresh CI runs started failing on master (and all open PRs) once 0.1.3 was published.

This patch swaps every call site over to the new name. The two functions compute the same value for any input that fits in u32; every existing call site passes a small literal (1, 3, 5, 10, 25, 50, 255, 454, 1000, 10_000), so no behavioural change.

All usages are in test/fixture code (src/wallet/coin_selection.rs test module, tests/wallet.rs, tests/build_fee_bump.rs) — no production code path was using the deprecated function.

Notes to the reviewers

• Pure mechanical rename; no logic or type changes.
• Unblocks CI on master and every open PR (e.g. fix(wallet): return error instead of panicking on invalid current_height #449, fix(wallet): exclude unconfirmed v3 outputs from non-v3 coin selection #442, fix(types): use bounds-checked access in Utxo::txout() for Foreign variant #445, fix(wallet): retry coin selection on NoChange to avoid dust/zero drai… #448).

Changelog notice

N/A — internal test-only change.

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran just p before pushing

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.21%. Comparing base (fbf803a) to head (be710a8).
⚠️ Report is 6 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #455   +/-   ##
=======================================
  Coverage   80.21%   80.21%           
=======================================
  Files          24       24           
  Lines        5347     5348    +1     
  Branches      242      242           
=======================================
+ Hits         4289     4290    +1     
  Misses        980      980           
  Partials       78       78           

Flag	Coverage Δ
rust	80.21% <ø> (+<0.01%)	⬆️

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[ValuedMammal]

ACK be710a8