Provide standard infrastructure for clearing global caches

[corona10]

It turns out that some global caches have memory leak issues while the refleak CI is running.
The global cache is not the problem, but we must provide a better solution to clear them after the tests.

Suggestion from @gvanrossum: #101988 (review)

[corona10]

cc @sobolevn

[gvanrossum]

Look hard, I think there is test infra code that handles a bunch of these. @JelleZijlstra ?

[sobolevn]

I know this cache-related helper:

cpython/Lib/test/libregrtest/utils.py

Line 116 in ed01add

def clear_caches():

[JelleZijlstra]

Thanks Nikita, I was just looking for that too.

I'm not sure we need any other general mechanism. If there's anything missing from libregrtest.utils.clear_caches, we should simply add it.

[gvanrossum]

That's the one I remembered.

[corona10]

Looks like #101988 should be ported to use libregrtest.utils.clear_caches
I will submit the patch soon.