GH-104584: Fix test_capi.test_counter_optimizer() when run twice

[vstinner]

test_counter_optimizer() and test_long_loop() of test_capi now create a new function at each call. Otherwise, the optimizer counters are not the expected values when the test is run more than once.

• Issue: Pluggable optimizer API #104584

[vstinner]

test_capi currently fails on the Refleaks buildbots:

0:45:19 load avg: 1.15 Re-running test_capi in verbose mode (matching: test_counter_optimizer, test_long_loop)
beginning 6 repetitions
123456
test_counter_optimizer (test.test_capi.test_misc.TestOptimizerAPI.test_counter_optimizer) ... ok
test_long_loop (test.test_capi.test_misc.TestOptimizerAPI.test_long_loop)
Check that we aren't confused by EXTENDED_ARG ... ok

----------------------------------------------------------------------
Ran 2 tests in 0.001s

OK
test_counter_optimizer (test.test_capi.test_misc.TestOptimizerAPI.test_counter_optimizer) ... FAIL
test_long_loop (test.test_capi.test_misc.TestOptimizerAPI.test_long_loop)
Check that we aren't confused by EXTENDED_ARG ... FAIL

======================================================================
FAIL: test_counter_optimizer (test.test_capi.test_misc.TestOptimizerAPI.test_counter_optimizer)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-x86_64.refleak/build/Lib/test/test_capi/test_misc.py", line 2386, in test_counter_optimizer
    self.assertEqual(opt.get_count(), 1000)
AssertionError: 0 != 1000

======================================================================
FAIL: test_long_loop (test.test_capi.test_misc.TestOptimizerAPI.test_long_loop)
Check that we aren't confused by EXTENDED_ARG
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/buildbot/buildarea/3.x.cstratak-RHEL8-x86_64.refleak/build/Lib/test/test_capi/test_misc.py", line 2408, in test_long_loop
    self.assertEqual(opt.get_count(), 10)
AssertionError: 0 != 10

----------------------------------------------------------------------
Ran 2 tests in 0.005s

FAILED (failures=2)
.test test_capi failed

cc @markshannon

[vstinner]

Reproduce the issue with: ./python -m test -m test_counter_optimizer -m test_long_loop -v test_capi test_capi command.

[vstinner]

Note: Python 3.12 is not affected.