Update to Python 3.13

[laggron42]

At the time of writing this issue, the MagicStack libs (uvloop, asyncpg, httptools) are not ready for 3.13 yet. Here is the list of linked issues and PRs:

• fails to build with Python 3.13 MagicStack/asyncpg#1181
• uvloop fails to build with Python 3.13-rc1 MagicStack/uvloop#622
• Not installing on Python 3.13 MagicStack/httptools#104
• Fix build and run tests on Python 3.13 MagicStack/httptools#107
• httptools 0.6.2 MagicStack/httptools#109