Hi team,

I'd like to propose adding Hypothesis as a test-time dependency. From the documentation:

Hypothesis is a Python library for creating unit tests which are simpler to write and more powerful when run, finding edge cases in your code you wouldn’t have thought to look for.

We write property-based tests all the time, but I think Hypothesis can help us write them faster and make them stronger. Apparently NumPy, pandas, and many other projects that use Hypothesis think so, too.

I imagine one of the concerns will be test duration, but this is no different from other parameterized tests, and we can use pytest markers (`slow`, `xslow`) to limit that as always.

Another concern would be nondeterminism in the CI suite. To address this, we've set up both a default deterministic profile and opt-in (via environment variable) nondeterministic profile.

Please let us know your thoughts here and in the PR:
https://github.com/scipy/scipy/pull/18927

Matt