fix(session): retry transcript writes after lock contention

[clabby]

Summary

• keep a session's transcript writer alive when SQLite reports temporary BUSY or LOCKED contention
• retry the blocked transaction after a short backoff so queued transcript records are committed after the lock clears
• retain the original persistence error when a writer fails permanently instead of reducing later appends to WriterStopped
• add regression coverage for resume after lock contention and for reporting the terminal writer error

Revision kustkunu fixes #188.

Testing

• cargo test -p tact transient_write_lock_preserves_transcript_for_resume
• cargo test -p tact stopped_writer_reports_its_persistence_error_to_later_appends
• cargo check

Closes #188

[codspeed-hq]

Merging this PR will not alter performance

✅ 18 untouched benchmarks
⏩ 31 skipped benchmarks¹

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_{Comparing cl/lock-fix (8d8d1af) with main (151a372)}

Footnotes

1. 31 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩