⚡ Bolt: Optimize ticker extraction in backtest hot loop

[toreleon]

💡 What: Replaced declarative array mapping, spreading, and Set initialization (Array.from(new Set([...held, ...discovery.candidates.map(...)])).slice(0, maxCandidates)) with imperative, bounded for loops and a tracking Set in the backtest runner.
🎯 Why: In hot loops like the backtest session runner, chaining array methods creates unnecessary intermediate arrays and causes GC overhead, even with small array sizes.
📊 Impact: Eliminates several intermediate array allocations per simulation turn, reducing GC pressure and slightly improving overall backtest execution speed.
🔬 Measurement: Verified correctness via pnpm test. The performance impact can be measured by running backtest benchmarks.

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PR created automatically by Jules for task 9308923854781300165 started by @toreleon

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[toreleon]

Closed in favor of #173.