fix: strip ANSI colors from logged exceptions

[heavry]

Closes #87

Summary

When exceptions are logged via Python's logging module, ANSI color escape codes appear as raw text in log files. This fix ensures:

• stderr output: keeps colored exceptions (terminal experience preserved)
• File/other handlers: exceptions are plain text without ANSI codes

Implementation

Modified better_exceptions/log.py to patch logging handlers differently based on type:

• StreamHandler targeting sys.stderr → uses colored format_exception
• All other handlers (FileHandler, etc.) → uses ExceptionFormatter(colored=False)

Changes

• better_exceptions/log.py — handler-aware color stripping
• test/test_file_logging.py — test verifying file output has no ANSI codes while stderr does

Acceptance criteria

• Logged exceptions to files do not contain ANSI color codes
• Terminal stderr output still shows colored exceptions
• Existing functionality preserved
• Test included