Optimize ffmpeg.py module functions and add unit tests

[michaelos443]

This PR optimizes the ffmpeg.py module functions, including get_usable_ffmpeg, generate_concat_list, ffmpeg_concat_av, and ffmpeg_concat_mp4_to_mpg. It also adds comprehensive unit tests for these functions.

Changes

• Improved error handling and logging in all functions
• Added detailed docstrings with clear explanations
• Enhanced version parsing logic in get_usable_ffmpeg
• Improved path handling for cross-platform compatibility in generate_concat_list
• Refactored ffmpeg_concat_av to reduce code duplication
• Optimized ffmpeg_concat_mp4_to_mpg with:
  • Better error handling with specific exception types
  • Improved file handling with proper cleanup of temporary files
  • Chunked file reading/writing to avoid loading entire files into memory
  • Validation of input files before processing
• Added unit tests for all functions

These optimizations improve code reliability, maintainability, and testability.

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Pull Request opened by Augment Code with guidance from the PR author

[michaelos443]

@Augment review