Rebuild evicted log indexes

[arukompas]

Summary

• force indexed readers to rescan when file metadata survives but the index cache is gone
• detect index chunks evicted from cache (while index metadata survives) lazily at read time — both rotated chunks and the current chunk — flag the index via rebuild_required metadata, and force a full rebuild on the next scan
• invalidate the memoized current chunk when index metadata is reloaded, so a forced rebuild doesn't double-count entries from the stale chunk definition
• add regression tests for evicted search index metadata/chunks, single evicted rotated chunks, and an evicted current chunk

Tests

• vendor/bin/pint --dirty
• vendor/bin/pest