Improve testing story for Python 3.14 and free-threading builds

[Zac-HD]

#4025 got some initial wins - like "running 3.14 in CI" and "ensuring that our auto-updates set up free-threading environments for us", but there's plenty more to do

• turn on CI for the free-threading builds (e.g. 3.13.0t-dev) and see what breaks. Might be blocked on upstream pydata packages for extensions? We also don't guarantee thread-safety at the moment, so I expect some chaos here and we might just turn the tests off again for a while.
• search for FIXME-py314 and... fix them
  • with the removal of typing.Bytestring, we no longer generate bytes instances from Sequence[int]; I think we probably should still do this
  • test_suggests_elements_instead_of_annotations is failing, so it seems something about dataclass introspection changed
  • some attrs introspection tests in Upgrade pinned dependencies #4069
• fix any other 3.14-specific issues that come up if or when they arise

[andfoy]

@Zac-HD I've been testing Hypothesis against the SciPy testsuite using the pytest-run-parallel (https://github.com/Quansight-Labs/pytest-run-parallel) plugin on 313t , which enables any test to be run concurrently using N threads.

Specifically, I've ran into issues originating from Hypothesis, which appear from time to time when using multiple threads to run this test:

            gc.collect()
            if not gc.get_referrers(r):
                if sys.getrefcount(r) <= _PLATFORM_REF_COUNT:
>                   raise ReferenceError(
                        f"`register_random` was passed `r={r}` which will be "
                        "garbage collected immediately after `register_random` creates a "
                        "weakref to it. This will prevent Hypothesis from managing this "
                        "PRNG. See the docs for `register_random` for more "
                        "details."
E                       ReferenceError: `register_random` was passed `r=<random.Random object at 0x4305a3f0a10>` which will be garbage collected immediately after `register_random` creates a weakref to it. This will prevent Hypothesis from managing this PRNG. See the docs for `register_random` for more details.

r          = <random.Random object at 0x4305a3f0a10>

../../../../.pyenv/versions/3.13.0rc1t/lib/python3.13t/site-packages/hypothesis/internal/entropy.py:123: ReferenceError

 def process_arguments_to_given(wrapped_test, arguments, kwargs, given_kwargs, params):
        selfy = None
        arguments, kwargs = convert_positional_arguments(wrapped_test, arguments, kwargs)
    
        # If the test function is a method of some kind, the bound object
        # will be the first named argument if there are any, otherwise the
        # first vararg (if any).
>       posargs = [p.name for p in params.values() if p.kind is p.POSITIONAL_OR_KEYWORD]
E       RecursionError: maximum recursion depth exceeded

arguments  = ()
given_kwargs = {'data': data(), 'dtype': sampled_from((<class 'numpy.float32'>, <class 'numpy.float64'>)), 'n_arrays': integers(min_value=1, max_value=3), 'p': floats(min_value=0, max_value=1), ...}
kwargs     = {'self': <scipy._lib.tests.test__util.TestLazywhere object at 0x4a0c3cc21d0>, 'xp': <module 'numpy' from '/home/andfoy/.pyenv/versions/3.13.0rc1t/lib/python3.13t/site-packages/numpy/__init__.py'>}
params     = mappingproxy(OrderedDict({'self': <Parameter "self">, 'xp': <Parameter "xp">}))
selfy      = None
wrapped_test = <function accept.<locals>.test_basic at 0x4a0c25f87a0>

../../../../.pyenv/versions/3.13.0rc1t/lib/python3.13t/site-packages/hypothesis/core.py:660: RecursionError

Other times, the test passes successfully, which suggests that some kind of race condition or non-isolation of parameters is occurring when running Hypothesis tests under parallel loads in the new free-threaded CPython. I wanted to ask you for any helpful pointers to help the project solve this kind of issues

[jobh]

@andfoy

The first one is probably a race here, or in a similar section,

hypothesis/hypothesis-python/src/hypothesis/internal/entropy.py

Lines 195 to 197 in e339c5f

	if hypothesis.core._hypothesis_global_random is None: # pragma: no cover
	hypothesis.core._hypothesis_global_random = random.Random()
	register_random(hypothesis.core._hypothesis_global_random)

where a second thread reassigns _hypothesis_global_random (and hence unreferences the first thread's random instance) before the first thread is finished registering it.

Fixable (if my guess is correct), but I suspect there may be many such cases and some of them may fail in less obvious ways...

[andfoy]

@jobh, thanks for the explanation! I've just opened a PR (#4094) that addresses this issue, which in turn enables the aforementioned test to be run successfully.

[Zac-HD]

3.14 is looking decent in this build, but I'm leaving disabled for now because the alphas do tend to break stuff pretty regularly.