Switching to using `puremagic` for identifying MIME types

What's Changed

• No need to keep multiple dirs for tests by @mindflayer in #245
• Back to testing doctest by @mindflayer in #246
• Pinning the version of aiohttp by @mindflayer in #248
• Test with the official stable Python 3.13 by @mindflayer in #253
• Switching to using puremagic for identifying MIME types by @mindflayer in #255

Full Changelog: 3.13.0...3.13.1