⚡ Optimize event log export to use async I/O

[ScottMorris]

💡 What:

• Refactored collect_event_logs in apps/threshold/src-tauri/src/event_logs.rs to be an async fn and use tauri::async_runtime::spawn_blocking for file reading and formatting.
• Extracted core log processing logic into a synchronous read_and_format_logs function to facilitate testing and isolation.
• Updated export_event_logs to be async, await collect_event_logs, and use spawn_blocking for directory creation and file writing.
• Updated get_event_logs to be async and await collect_event_logs.
• Added a unit test read_and_format_logs_works to verify the logic.

🎯 Why:

• The previous implementation performed synchronous file I/O on the main thread, which could cause UI freezes, especially with large log files.
• Offloading these operations to a worker thread via spawn_blocking ensures the application remains responsive during log export.

📊 Measured Improvement:

• Verified that the new implementation correctly passes tests and compiles.
• While exact UI responsiveness metrics were not collected (requires UI interaction), offloading I/O from the main thread is a standard and proven performance optimization in Tauri applications.

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PR created automatically by Jules for task 6279845040915257839 started by @ScottMorris

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