Update deprecated modules and improve compatibility + ordering flatte…

[kh813]

Based on the Maintain ordering in flattened SPF record

Update deprecated modules and improve compatibility

[kh813]

Thank you for creating this useful SPF flattening tool!

I've updated the code to address the deprecation warnings and improve Python 3.12+ compatibility:

Changes made:

• Replaced deprecated imp module with importlib
• Updated DNS resolver error handling for better compatibility
• Improved exception handling throughout the code
• Maintained backward compatibility where possible

Testing:

• Tested on Python 3.8, 3.10, and 3.12
• Verified all existing functionality works as expected
• No breaking changes to the public API

The code now runs without deprecation warnings on modern Python versions while maintaining the same functionality. All existing features and command-line options remain unchanged.

Feel free to review and let me know if you'd like any adjustments!