fix: make no-op deleteBefore advance cursor in commitQCState and simplify deleteBefore API

[wen-coding]

Summary

• In no-op mode (persistence disabled), commitQCState.deleteBefore returned early without advancing s.next. When MaybePruneAndPersist was called with both an anchor and commitQCs, the anchor's persistCommitQC would fail with "out of sequence" because the cursor was stale.
• Fix by ensuring the cursor advances regardless of whether a WAL is present.
• Remove the redundant idx parameter from deleteBefore — in production, idx was always derived from the anchor's CommitQC.Index(). The new signature is deleteBefore(anchor *types.CommitQC).
• Refactor tests to go through the production API (anchors) instead of internal truncation-only calls. Crash recovery tests now simulate crashes via WAL file manipulation rather than calling internal methods directly.
• Improve no-op tests for blocks and commitqcs persisters to exercise prune-then-persist paths that would have caught this.

Test plan

• TestNoOpCommitQCPersister persists QCs, prunes with a future anchor, then appends more — verifies cursor advances correctly in no-op mode
• TestNoOpBlockPersister exercises multiple MaybePruneAndPersistLane calls verifying afterEach callbacks fire in no-op mode
• TestCommitQCDeleteBeforePastAllCrashRecovery and TestCommitQCDeleteBeforeWithAnchorRecovers now simulate crashes via clearCommitQCWAL instead of internal API
• All existing persist tests pass

[github-actions]

The latest Buf updates on your PR. Results from workflow Buf / buf (pull_request).

Build	Format	Lint	Breaking	Updated (UTC)
✅ passed	✅ passed	✅ passed	✅ passed	Mar 26, 2026, 3:43 PM

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 58.58%. Comparing base (78c53dd) to head (e3e6b07).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...t/internal/autobahn/consensus/persist/commitqcs.go	83.33%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3122      +/-   ##
==========================================
- Coverage   58.58%   58.58%   -0.01%     
==========================================
  Files        2099     2099              
  Lines      173525   173522       -3     
==========================================
- Hits       101657   101654       -3     
  Misses      62805    62805              
  Partials     9063     9063              

Flag	Coverage Δ
sei-chain-pr	75.11% <83.33%> (?)
sei-db	70.41% <ø> (ø)

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Files with missing lines	Coverage Δ
...t/internal/autobahn/consensus/persist/commitqcs.go	77.38% <83.33%> (-0.78%)	⬇️

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