Improve Test Coverage to 100%

[0xarchit]

The current test suite has several gaps and failing tests. This issue tracks the effort to achieve 100% test coverage across all Rust modules, including settings, timer logic, and system integrations.
Key tasks:

1. Fix existing failing tests in settings_tests.rs.
2. Add unit tests for events.rs, system.rs, and updater.rs.
3. Implement integration tests for the tray and main event loop where possible.