CPython 3.14 and Cython==3.1.0 CI issues

Tracking issue for the skipifs & pinning added in #3264

• https://github.com/cython/cython/issues/6865 Cython==3.1.0 broke line tracing/code coverage on async code. Fixed on master, so we're only waiting for a new release. The version is pinned in tox.ini and ci.yml
• https://github.com/python/cpython/issues/133932 broke test_run.test_error_in_run_loop which is marked with a skipif
• Jedi, mypy, pyright & pylint all have incomplete support for 3.14 so test_static_tool_sees_all_symbols and test_static_tool_sees_class_members are marked with skipif.
  • we could start adding tool-specific logic once they start supporting 3.14, but these aren't critical tests to run on every version imo
• https://github.com/python/cpython/issues/133779 windows+cffi+3.14 is completely broken and the run doesn't start at all, so continue-on-error has been enabled for windows 3.14. Should be fixed in beta 2.
• https://github.com/python/cpython/issues/125603 see https://github.com/python-trio/trio/issues/3209

Start with the CPython issue 125603 and the linked Trio issue 3209, then inspect the existing skipifs and pinning in tox.ini and ci.yml. Done means resolving the remaining Python 3.14 compatibility problem and updating the CI configuration accordingly, with the relevant checks passing.