Replaced Lua's built-in dofile-based loading with RapidJSON for reading and writing highlights data. This significantly improves synchronization speed on older or resource-constrained devices.
- Added robust fallback handling for missing or invalid files.
- Improved merge logic efficiency.
- Ensured updated highlights are reloaded correctly in KOReader UI.
This change reduces UI blocking and lag during sync operations, especially on e-readers with slower CPUs.