perf: use foldhash for log-replay file dedup set

[DrakeLin]

What changes are proposed in this pull request?

Swap the std HashSet used to track seen (path, dv_unique_id) pairs during log replay for a HashSet backed by foldhash::fast::RandomState. This is the hottest hash structure on the read path: every Add/Remove across every commit and every action in every checkpoint hits a contains and (for commit batches) an insert. SipHash-1-3 (the std default) is ~2x slower than foldhash on small keys for no functional benefit here.

The alternate hasher is hidden behind a crate-private SeenFileKeys type alias. SerializableScanState.seen_file_keys keeps its existing HashSet<FileActionKey> (std hasher) so the distributed-scan wire format and public API are unchanged; conversion happens once per phase boundary.

foldhash::fast::RandomState reseeds per-process, so HashDoS resistance for path keys read from the Delta log is preserved.

How was this change tested?

• cargo nextest run -p delta_kernel --all-features (4704 tests pass)
• cargo clippy --workspace --benches --tests --all-features -- -D warnings
• cargo doc --workspace --all-features --no-deps

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.85%. Comparing base (0003a4e) to head (00206bd).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2698      +/-   ##
==========================================
- Coverage   88.85%   88.85%   -0.01%     
==========================================
  Files         199      199              
  Lines       64673    64820     +147     
  Branches    64673    64820     +147     
==========================================
+ Hits        57465    57595     +130     
- Misses       5022     5027       +5     
- Partials     2186     2198      +12     

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[github-actions]

Benchmark results

_{Commit: 00206bd · Trigger: auto-push · Tags: base}

Test	Base	PR	Change
101kAdds1kCommitsSinceChkpt1Chkpt/readLatest/readMetadata/serial	328.2±4.15ms	325.2±5.78ms	1.01x faster
101kAdds1kCommitsSinceChkpt1Chkpt/readV10/readMetadata/serial	1572.8±44.24µs	1601.7±39.77µs	1.02x slower
101kAdds1kCommitsSinceChkpt1Chkpt/readV110/readMetadata/serial	33.7±0.49ms	33.3±0.79ms	1.01x faster
101kAdds1kCommitsSinceChkpt1Chkpt/readV210/readMetadata/serial	65.8±1.12ms	67.5±4.90ms	1.03x slower
101kAdds1kCommitsSinceChkpt1Chkpt/readV510/readMetadata/serial	163.6±3.11ms	159.1±2.91ms	1.03x faster
101kAdds1kCommitsSinceChkpt1Chkpt/readV60/readMetadata/serial	17.7±0.25ms	17.3±0.26ms	1.02x faster
101kAdds1kCommitsSinceChkpt1Chkpt/snapshotLatest/snapshotConstruction	113.7±2.39ms	114.2±3.08ms	1.00x slower
101kAdds1kCommitsSinceChkpt1Chkpt/snapshotV10/snapshotConstruction	29.4±0.20ms	29.4±0.65ms	1.00x
101kAdds1kCommitsSinceChkpt1Chkpt/snapshotV110/snapshotConstruction	38.4±0.69ms	37.9±0.42ms	1.01x faster
101kAdds1kCommitsSinceChkpt1Chkpt/snapshotV210/snapshotConstruction	47.3±0.75ms	47.1±0.98ms	1.00x faster
101kAdds1kCommitsSinceChkpt1Chkpt/snapshotV510/snapshotConstruction	73.5±1.97ms	74.0±1.71ms	1.01x slower
101kAdds1kCommitsSinceChkpt1Chkpt/snapshotV60/snapshotConstruction	33.9±0.36ms	33.6±0.33ms	1.01x faster