Enable mwparserfromhell for use with thread-free Python releases

[xqt]

Running Python 3.13t (the thread-free variant of Python 3.13 without GIL restriction) gives the following warning:

<frozen importlib._bootstrap>:488: RuntimeWarning: The global interpreter lock (GIL) has been enabled to load module 'mwparserfromhell.parser._tokenizer', which has not declared that it can run safely without the GIL. To override this behavior and keep the GIL disabled (at your own risk), run with PYTHON_GIL=0 or -Xgil=0.

See pre-tests: https://github.com/xqt/pwb/actions/runs/18751830436/job/53493241287
See also: #181

[earwig]

https://docs.python.org/3/howto/free-threading-extensions.html
Will need to test obviously, but I think things should mostly just work if we enable it.