⚡ Bolt: Optimize candidate subset extraction in backtest hot loop

[toreleon]

💡 What: Replaced an expensive array-to-Set-to-array method chain (Array.from(new Set([...held, ...discovery.candidates.map(c => c.ticker)])).slice(0, N)) with bounded for loops and a dedicated Set for duplicate tracking.
🎯 Why: The previous approach allocated multiple intermediate arrays and iterated over the entire candidate list on every tick of a backtest session, generating significant garbage collection overhead.
📊 Impact: Reduces memory allocations in the main backtest simulation loop, leading to faster execution times for multi-month backtest runs, with fewer allocations per turn.
🔬 Measurement: Verify tests run successfully using pnpm test and types pass with pnpm typecheck. Inspect the loop logic in src/agent/backtestRunner.ts to see that it processes elements lazy and exits early.

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PR created automatically by Jules for task 3183424267232562118 started by @toreleon

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