Upgrade Python and GitHub Actions versions

[cclauss]

Related to:

• Support the free-threaded build of Python 3.13/3.14 #116

[ngoldbaum]

This PR also needs something like this for srsly to become installable:

diff --git a/setup.cfg b/setup.cfg
index 350d943..fe5f34a 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -27,7 +27,7 @@ classifiers =
 [options]
 zip_safe = true
 include_package_data = true
-python_requires = >=3.9,<3.14
+python_requires = >=3.9,<3.15
 setup_requires =
     cython>=0.29.1
 install_requires =

[cclauss]

• Document why uv discards upper bounds on requires-python astral-sh/uv#15927

[crusaderky]

the ujson segfault on 3.14 is highly concerning. I'd rather go the way of #119 + #120.

[cclauss]

• Refresh CI to a sane point #119
• DNM unvendor all libraries #120