Add Python 3.12 support, remove Python 3.7 support

[alex-cloudmix]

• Allow Python minor versions beyond 3.11
• Add av version constraint of ^11.0.0 (earlier versions fail to install with Python 3.12)
• Set pyee version constraint to ^11.1.0 (9.0.4 causes a segfault when aiortc is imported with Python 3.12)
• Disallow Python 3.7 (not supported by pyee 11.1.0)
• Use raw strings for regex patterns (fixes invalid escape sequences, which generate SyntaxWarning warnings in Python 3.12)

Note: SyntaxWarning warnings are also generated by pymediasoup's sdp-transform dependency. This is fixed by https://github.com/skymaze/sdp-transform/pull/6. ~Once https://github.com/skymaze/sdp-transform/pull/6 is merged and released, this PR should be updated to use the new release of sdp-transform before merging.~ sdp-transform version has now been updated.