TST: add a custom pytest session header to make runtime state (free-threading, JIT) visible

[neutrinoceros]

runtime-introspect is a tiny library authored by yours truly. It's also distributed on conda-forge.

[neutrinoceros]

to my surprise, the header still doesn't appear here even after #566. I'm wondering if an embedded conftest.py is just not collected in time for this hook to have a visible effect.

[neutrinoceros]

Indeed, per the documentation

This hook is only called for initial conftests.

though from what I grasp, bottleneck/conftest.py should still be picked up as an "initial" conftest, as it lives in the parent directory to bottleneck/tests. It's possible the phrasing is just misleading, or that the discovery logic is actually broken in pytest itself.

[neutrinoceros]

pytest-dev/pytest#14557

[neutrinoceros]

#573 makes this work as expected for pytest ., but not with --pyargs. I don't think CI should only exercise this mode, and I'd be in favor of changing our primary way to run tests to the default pytest mode.