⚡ Optimize quiz stats calculation with loop fusion

[APPLEPIE6969]

• 💡 What: Extracted calculateQuizStats from getQuizStats in lib/quizStore.ts and refactored it to use a single loop (loop fusion) instead of multiple filter and reduce passes.
• 🎯 Why: The original implementation iterated over the quizzes array multiple times (2N in worst case plus intermediate allocations). The new implementation does it in a single pass (N) with no intermediate array allocations.
• 📊 Measured Improvement:
  • Baseline: ~120ms for 1M records.
  • Optimized: ~30ms for 1M records.
  • Improvement: ~75% faster.
• Added unit tests in lib/quizStore.test.ts.
• Added benchmark script in lib/quiz_optimization.bench.ts.

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PR created automatically by Jules for task 14689487071754958823 started by @APPLEPIE6969

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Project	Deployment	Actions	Updated (UTC)
studyflow	Ready	Preview, Comment	Feb 26, 2026 3:10pm