Ensure Single Data Load Feeds Grid Optimizer (Cache Contract)

[Muratich]

Depends: #118 , #111

GridOptimizer runs hundreds of backtests — price data must be loaded once and reused.

Scope:

• Verify CandleCache / DB path: first load populates cache; subsequent reads in same process hit cache
• Add integration note or test: simulate N strategy runs on same (instrument, timeframe) → no duplicate broker fetch (when data already in DB)
• If gap found: fix cache key or expose ensure_candles_loaded() for optimizer entrypoint

Definition of Done:

• Documented contract: "optimizer receives pre-loaded price series, does not call broker"
• Test or scripted check demonstrating cache reuse
• Samy confirms GridOptimizer receives in-memory series, not re-fetching per combo