fix(planner): model count-min sketch heap costs

[milindsrivastava1997]

Closes #651

Summary

• Wire CountMinSketchWithHeap into atomic cost resolution using the regular-path/top-k benchmark reference.
• Scale CPU costs linearly from heap size 32 and model runtime memory analytically.
• Warn and drop candidates when reference data is missing or malformed, preserving EXACT fallback.
• Add per-candidate cost measurements and regression coverage.
• Update the optimizer implementation-plan status.

Verification

• cargo clippy -p asap_planner --all-targets -- -D warnings
• cargo test --workspace -- --test-threads=1