Provide option to omit timezone from output if UTC

I added an ignore_timezone_if_UTC option to omit the timezone if it's set to UTC, aligning with the issue's proposal. The option is enabled by default and integrated into the timezone extraction and formatting logic.

Thanks for your work on this. It needed a little massaging, and it also turns out that the timezones weren't (ever?) being passed to the format method in the expected structure.

Automatically closed - issue fixed for 2 weeks with no activity.