docs: update performance.md benchmark tables after perf sprint

[abix-]

Type

• docs

Severity

Low

Problem

The benchmark tables in docs/performance.md:468-503 show pre-optimization numbers from 2026-03-14 (commit d507a1e). Several systems have been optimized since:

• arrival_system: ReturningSet gives ~77% improvement at 50K (Codex reported)
• build_selection_overlay: DirectControlSet avoids 50K NPC scan
• Projectile deactivation: O(1) via reverse index
• Path invalidation: precomputed chunks
• Farm marker despawn: O(1) via slot->entity map
• Tower system: eliminated Vec clone

Per performance.md PR Review Procedure #4: 'Add/adjust microbenchmarks for modified hotspots.'

Fix

Run cargo bench --bench system_bench and update the benchmark tables with current numbers. Update the Budget Summary if totals changed materially.

Acceptance Criteria

• Benchmark tables reflect post-optimization numbers
• Budget Summary updated
• Last-run date updated

[abix-]

Claude

• Changed: none
• Tests: n/a
• Open: benchmarks deferred -- user decision to skip benching for now
• State: claimed -> waiting
• Next: run cargo bench when ready, update tables