Benchmark variable-arity sequence tables

[ezrosent]

Summary

• Add Divan microbenchmarks comparing fixed-arity SequenceTable workloads with SortedWritesTable.
• Measure serial and parallel insert, delete, rebuild, and compaction costs, both merge-only and end-to-end.
• Add wide-sequence benchmarks for index construction and sparse/high-fanout indexed rebuilds.
• Run locally with cargo bench -p egglog-core-relations --bench sequence_table.

Stack

Draft, stacked on #975. This is PR 3 of 12 in the sequence-backed container stack.

Validation

Validated on the complete 12-commit stack:

• cargo nextest run --workspace: 1,362 tests passed
• cargo test --workspace --doc
• cargo clippy --workspace --all-targets -- -D warnings
• cargo fmt --all -- --check

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (codex/inline-containers-02-sequence-indexes@c6a903a). Learn more about missing BASE report.

Additional details and impacted files

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[codspeed-hq]

Merging this PR will not alter performance

✅ 37 untouched benchmarks
⏩ 227 skipped benchmarks¹

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_{Comparing codex/inline-containers-03-sequence-benchmarks (fd5fa6f) with codex/inline-containers-02-sequence-indexes (c6a903a)}

Footnotes

1. 227 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. ↩