[Meta] Research: what can we test with Hypothesis?

We now have both the code and CI job to run hypothesis tests.

In this issue I invite everyone to propose ideas: what can we test with it?
Criteria:

1. Tests should be suitable for property-based nature of hypothesis
2. The action under test should be fast and reliable (since hypothesis will produce a lot of cases to tests, we cannot do any slow / network related things)
3. Strategies for data generation should be rather simple (I think that later we can get to more complex strategies, but for now for the sake of simplicity and maintability I propose not to get too crazy with them)

What else?

Known applications

Property-based tests are great when there are certain patterns:

• decode and encode
• dumps and loads

There are also some hidden patterns as (example):

• If 'a' in s then
• s.index('a') must return an integer

Existing work

Good examples of exising stuff:

• Existing hypothesis tests in test_zoneinfo by @pganssle
• Existing tests in https://github.com/Zac-HD/stdlib-property-tests by @Zac-HD and others

Linked PRs

• gh-107862: Add roundtrip hypothesis tests to test_binascii #107863
• gh-107862: Add property-based round-trip tests for base64 #119406
• gh-107862: Add property tests for strftime/strptime #124550