Add preserve_formatting config option to prevent automatic subtitle processing that strips formatting tags and styling. When enabled (default: true), WebVTT files skip pycaption read/write cycle to preserve tags like <i>, <b>, positioning, and other formatting.
- Add pysubs2 as default conversion method for 'auto' mode
- Add support for MicroDVD (.sub), MPL2 (.mpl2), and TMP (.tmp) formats
- Implement convert_with_pysubs2() method with fallback to standard conversion
- Update from_mime() to handle new subtitle format types
- Map all supported formats to pysubs2 format identifiers
- Update docstrings to reflect new capabilities
