[3.13] gh-109700: Improve stress tests for interpreter creation (GH-109946) (GH-133391)

* Ensure that destructors are called in the test that created interpreters, not after finishing it.
* Try to create/run interpreters in threads simultaneously.
* Mark tests that requires over 6GB of memory with bigmemtest.
(cherry picked from commit 61b50a98b42a75a66ec52d78811b32e70220bcaf)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>