Release and declare support for Python 3.13

[skynavga]

In particular, Python 3.13 is not presently listed in the classifiers in pyproject.toml.

Lack of documented support is preventing updates to Python 3.13 on projects for which asyncpg is a production (non-development) dependency.

[dangbert]

looks like this was completed in v0.3.0 via #1188

https://github.com/MagicStack/asyncpg/releases/tag/v0.30.0

Edit: ah but indeed it's not listed where you linked to

[skynavga]

@dangbert exactly; as shown in pypi.org under Programming Language