Add support for Python 3.13, and release 3.13.0.

The default Python version remains unchanged (at 3.12.x) for now.

Notably for Python 3.13 we now:
- No longer install setuptools and wheel - matching what the wider
  ecosystem has already done for Python 3.12+.
  (See the Python CNB's removal PR for more details:
  heroku/buildpacks-python#243)
- No longer install the SQLite headers and CLI, as the first step
  towards dropping that rarely used feature.

In addition, for all Python versions we now also remove the `idle3`
and `pydoc3` scripts, since they do not work with relocated Python
and so have been broken for some time. Their functionality continues
to be available by invoking them via their modules instead (e.g.
`python -m pydoc`).

Release announcement:
https://blog.python.org/2024/10/python-3130-final-released.html
https://www.python.org/downloads/release/python-3130/

Details on what's new in Python 3.13:
https://docs.python.org/3.13/whatsnew/3.13.html

Binary builds:
https://github.com/heroku/heroku-buildpack-python/actions/runs/11259777638

Python 3.13 readiness status of the top 360 packages on PyPI:
https://pyreadiness.org/3.13/

GUS-W-14846826.
GUS-W-14846839.
GUS-W-16944574.