Fix free-threaded Python 3.14t compilation and thread safety

[jensens]

• Replace callable->ob_refcnt with Py_REFCNT(callable) macro
• Guard im_self mutation optimization with #ifndef Py_GIL_DISABLED (not thread-safe without GIL)
• Add 3.14t to CI matrix (Linux), tox envlist, and .meta.toml

Fixes #88

[davisagli]

The C change LGTM.

Still needs to be updated with zopefoundation/meta#389

[jensens]

The C change LGTM.

Still needs to be updated with zopefoundation/meta#389

updated

[jensens]

updated zope meta again

[dataflake]

I'll just add this as a comment: I have zero knowledge of those C bits. But the rest LGTM...

[jensens]

I'll just add this as a comment: I have zero knowledge of those C bits. But the rest LGTM...

Making it work for FT is mostly about using macros/apis for specific GIL related tasks, like reference counting and avoiding to rely on the GIL for thread safety, most chnages are straight forward:

• Py_REFCNT() / Py_SET_REFCNT() instead of direct ob_refcnt access
• Py_TYPE() / Py_SET_TYPE() instead of direct ob_type access
• Py_BEGIN_CRITICAL_SECTION / Py_END_CRITICAL_SECTION to protect mutable state
• PyMutex for custom locking

Full Info: https://docs.python.org/3.14/howto/free-threading-extensions.html

[dataflake]

I'm going to approve this now because there seems no progress at all from the other reviewers.

I looked at the C changes and from eyeballing it those seem to make sense.