Refactor Session File Management

[codenamev]

Changes

• Moved file management logic from PodcastBuddy module to Session class
• Added proper tests for Session file management methods
• Updated type signatures in RBS file
• Maintained backward compatibility through delegation methods

Why

This refactoring improves the codebase by:

1. Following Single Responsibility Principle - Session now fully manages its files
2. Making the code more maintainable and testable
3. Preparing for future refactoring by establishing clear boundaries

Testing

• Added comprehensive tests for Session file management
• All existing tests pass
• Manual testing of file operations completed

Notes

This is part of our ongoing effort to improve the object-oriented design of the codebase. The changes are backward compatible, so no updates are required for existing code.