Add TestCase duration filters to case search

[absalonCRC]

Summary

• add setup/testing/expected duration min/max filters to /cases/search/
• normalize duration RPC filter values so search UI seconds and API duration strings work with DurationField lookups
• annotate expected_duration for TestCase.filter so it can be filtered the same way it is returned

Testing

• LC_ALL=en_US.UTF-8 LANG=en_US.UTF-8 .venv/bin/python manage.py test -v2 --noinput --settings=tcms.settings.test tcms.rpc.tests.test_testcase.TestCaseFilter tcms.testcases.tests.test_views.TestSearchCases
• git diff --check

Closes #1923.

[atodorov]

Stop the AI slop.

Duplicate of #4357