Add unit tests for ydotool injector

[Coldaine]

Issue Description

The ydotool injector in src/ydotool_injector.rs lacks unit tests and needs comprehensive test coverage.

Current State

• No unit tests for ydotool_injector.rs
• Only relies on potential integration tests that are disabled
• Functionality cannot be verified through automated tests

Requirements

1. Add comprehensive unit tests for all ydotool injector methods
2. Mock dependencies and system calls for reliable testing
3. Test both success and error scenarios
4. Verify clipboard operations and paste functionality

Benefits

• Better code coverage
• Easier to catch regressions in ydotool functionality
• Improved reliability of Linux Wayland/clipboard injection
• Better developer experience for contributors

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.