Chunk very long commands when writing file.

[MarcCote]

This pull request introduces improvements to file writing in the workspace and enhances the logger's debug mode activation. The most significant changes are the addition of chunked file writing to handle large contents, more robust detection of debug mode via environment variables, and expanded test coverage for edge cases in file writing.

Workspace file writing improvements:

• The write_file method in debug_gym/gym/workspace.py now splits content into 32kB chunks when writing to files, ensuring compatibility with shell command length limits and supporting very large files.

Logger enhancements:

• The debug mode in debug_gym/logger.py is now activated if the DEBUG_GYM_DEBUG environment variable matches common truthy values like "1", "true", "yes", or "on", making it more flexible and user-friendly.

Test coverage improvements:

• The test test_write_file in tests/gym/test_workspace.py now includes checks for writing empty content and very large content (2MB), verifying that the new chunked writing logic works correctly for these edge cases.

Closes #245