[3.13] gh-124402: Speed up test_free_threading and test_super (#124491) (#124585)

gh-124402: Speed up test_free_threading and test_super (#124491)

* Reduce the number of iterations and the number of threads so a
  whole test file takes less than a minute.
* Refactor test_racing_iter_extend() to remove two levels of
  indentation.
* test_monitoring() uses a sleep of 100 ms instead of 1 second.

(cherry picked from commit 0387c34f7c91428681ca8a4ba4e3d22b9acffde4)