feat(wal): expose AllowEmpty config and add TruncateAll method

[wen-coding]

Summary

• Adds AllowEmpty bool to wal.Config and passes it through to tidwall/wal.Options, enabling callers to permit a fully empty log after truncation.
• Adds TruncateAll() method to WAL[T] that removes all entries in a single call. No-ops on an already-empty log; returns an error if AllowEmpty is not set.
• This enables the autobahn persistence layer to clear a WAL in-place (e.g. when the prune anchor advances past all persisted entries) instead of the heavier close → remove directory → reopen pattern currently used in indexedWAL.Reset().

Test plan

• TestTruncateAll — writes entries, truncates all, verifies empty state, writes new entries, reopens and verifies continuity
• TestTruncateAllWithoutAllowEmpty — confirms TruncateAll returns an error when AllowEmpty is not set
• TestTruncateAllOnEmptyLog — confirms no-op on an already-empty log
• Full existing test suite passes (29/29)

[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 11, 2026, 2:48 PM

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.36%. Comparing base (2bb2537) to head (edb4a81).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sei-db/wal/wal.go	50.00%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3049      +/-   ##
==========================================
+ Coverage   58.33%   58.36%   +0.02%     
==========================================
  Files        2079     2080       +1     
  Lines      171885   171733     -152     
==========================================
- Hits       100268   100229      -39     
+ Misses      62671    62577      -94     
+ Partials     8946     8927      -19     

Flag	Coverage Δ
sei-chain-pr	67.34% <50.00%> (?)
sei-db	70.41% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
sei-db/wal/wal.go	68.65% <50.00%> (+0.12%)	⬆️

... and 37 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.