bench(compaction): expand scenario matrix (read-while-compaction, write-vs-frequency)

[belveryin]

Summary

Expand compaction benchmark coverage beyond baseline/post-compaction into concurrent and sweep scenarios.

Motivation

We need workload realism for compaction tradeoff analysis, especially tail impact and ingest interference.

Scope

• Add scenarios:
  • read_while_compaction
  • write_throughput_vs_compaction_frequency
  • optional mixed read/write tail-latency scenario
• Add sweeps for selected compaction knobs:
  • l0 trigger
  • max inputs
  • max task bytes
• Keep deterministic seeds and fixed dataset tiers.

Acceptance Criteria

1. New scenarios run locally with stable config surface.
2. JSON includes scenario-specific sweep dimensions.
3. Docs include reproducibility guidance.

Out of Scope

• Real S3 backend automation in the same PR.

Labels

performance, benchmark, compaction

[linear]

DEV-524