gh-86275: improve Hypothesis configuration for CI and local runs

[Zac-HD]

Per #22863 (comment), this PR configures Hypothesis to ignore unexpectedly slow tests. Relative to the default of failing, this reduces flakiness due to variable performance of CI machines.

The second commit adds caching to the CI test run, so that if a CI run finds a rare but real failure that input will be replayed in future CI runs (at least until the cache expires, or the test passes and Hypothesis discards the now-passing input). This doesn't come up often, but if it does will convert flaky tests into reliable failures.

Third, we can upload the database as an "artifact" from CI and configure local runs to use that as a pull-through cache - meaning that "reproducing a failure from CI" is just "run the tests locally". No impact on flakiness but it's a rather nice workflow! ¹

cc @pganssle for review / checking that it works on your machine

• Issue: Use hypothesis for testing the standard library, falling back to stubs #86275

Footnotes

1. Unfortunately the 'dump a patch with explicit examples' workflow relies on libcst and our pytest plugin - if this would be particularly interesting we can talk about making it work with unittest and perhaps even ast. ↩

[AlexWaygood]

The CI on this PR is currently failing to start due to invalid workflow syntax:

https://github.com/python/cpython/actions/runs/4977097067

The workflow is not valid. .github/workflows/build.yml (Line: 378, Col: 11): A sequence was not expected

[bedevere-bot]

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

[Zac-HD]

I have made the requested changes; please review again.

[bedevere-bot]

Thanks for making the requested changes!

@AlexWaygood: please review the changes made to this pull request.

It's valid syntax now

[webknjaz]

@Zac-HD did you mean to keep that leading hyphen?

[webknjaz]

This makes it look up the '- hypothesis-database-' prefix, and I'm pretty sure you wanted 'hypothesis-database-':

Cache not found for input keys: hypothesis-database-9927179210, - hypothesis-database-

(https://github.com/python/cpython/actions/runs/9927179210/job/27421821417#step:21:24)

[webknjaz]

@Zac-HD here's the fix: #121756