⚡ Optimize LibraryRepository.updateReadingMode

[Aatricks]

💡 What: Replaced the inefficient in-memory filtering and updating of library items in updateReadingMode with a direct SQL update query in LibraryDao.

🎯 Why: The previous implementation loaded the entire library into memory to update the reading mode for a group of chapters (grouped by baseTitle). This caused unnecessary memory overhead and CPU usage, especially for large libraries.

📊 Measured Improvement:

• Baseline: The original implementation performed a full table scan (getAllItems), filtered the list in memory, and then executed a batch insert (insertItems).
• Optimization: The new implementation executes a single SQL UPDATE statement targeting only the relevant rows.
• Verification: A benchmark test confirmed that getAllItems is never called during the execution of the optimized method, proving the elimination of the O(N) memory load. All existing unit tests passed.

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PR created automatically by Jules for task 16969642914540689963 started by @Aatricks

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