perf(turbo-persistence): shard meta files by family (#97703)
## Summary
- Store live meta files in primary per-family shards so queries avoid
unrelated-family metadata
- Consolidate live metadata during compaction, retire subsumed meta
files in the same commit, and retain merged used-key-hash AMQFs.
- Add debug assertions for shard ownership/order and compaction
precedence invariants.
## Performance
Paired `LARGE_DB=1` Criterion binaries were run interleaved on the same
machine to reduce host drift.
| Scenario | Canary | PR | Result |
| --- | ---: | ---: | --- |
| Four-family cached `get` miss (100 metas/family) | 2.40–2.55 µs |
2.11–2.21 µs | **~10–12% faster** |
| Existing single-family cached `get` miss | 1.93–2.12 µs | 2.00–2.04 µs
| Neutral within run-to-run noise (~+0.5% on means) |
| Existing full compaction (4 Mi entries, 8 commits) | ~624 ms | ~624 ms
| Neutral in the stable paired run; repeated samples stayed within
normal noise |
Read hits should see a small improvement but it isn't measurable, misses
are the major benefit.
## Verification
- `cargo test -p turbo-persistence`
- `cargo test -p turbo-persistence --features stats`
- `cargo clippy -p turbo-persistence --all-targets --features stats --
-D warnings`
- `LARGE_DB=1` interleaved Criterion A/B runs
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Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Luke Sandberg <210140+lukesandberg@users.noreply.github.com>
