feat: add AdjustExistingTrackDrift use case to adjust drift scale of existing tracks

- Implemented AdjustExistingTrackDrift struct with execute method to modify drift scale of existing tracks in a project.
- Added tests for adjusting drift scale, handling non-existent track IDs, and invalid scale values.
- Updated MediaTrackInfo and AudioTrack entities to include drift_scale field.
- Enhanced Project entity with needs_mkvmerge method to determine if mkvmerge is required based on drift scale.
- Integrated drift scale adjustments into existing track list UI, allowing users to modify drift values.
- Updated various use cases and UI components to support drift scale functionality, including add audio/subtitle forms and batch processing.
- Implemented mkvmerge availability check and integrated it into the application workflow for conditional processing.

src/adapters/mkvmerge/mod.rs

@@ -0,0 +1,5 @@
+pub mod command_builder;
+pub mod mkvmerge_gateway;
+
+pub use command_builder::MkvmergeCommandBuilder;
+pub use mkvmerge_gateway::MkvmergeGateway;