⚡ Bolt: Optimize ticker deduplication array allocations in backtests

[toreleon]

💡 What: Replaced chained .map(), spreads, new Set(), Array.from(), and .slice() operations in src/agent/backtestRunner.ts with an imperative, bounded for loop for deduplicating ticker lists.
🎯 Why: In the hot path of backtests, these chained operations create multiple intermediate arrays (allocating O(N) memory where N is total positions + candidates). This causes significant garbage collection overhead during large backtests. The bounded loop reduces this to an O(K) complexity based on the early exit mechanism (where K is maxCandidates).
📊 Impact: Noticeably reduced memory allocation and GC pressure inside the runBacktestSession loop by removing 5 intermediate array allocations per interval turn, which directly improves backtesting run time.
🔬 Measurement: Verify via running pnpm test tests/tui.test.tsx (the backtest streaming tests should execute properly with similar or lower test latencies). Run pnpm typecheck to ensure type-safe behavior.

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PR created automatically by Jules for task 4520440390076821137 started by @toreleon

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