Function HandleFileEvent 

pub async fn HandleFileEvent(
    event: Event,
    index_arc: &RwLock<FileIndex>,
    config: &IndexingConfig,
) -> Result<()>

Handle file watcher event for incremental indexing

This function processes file system events and updates the index accordingly:

• File Created: Index the new file
• File Modified: Re-index the modified file
• File Removed: Remove from index