test_netrc, test_pep646_syntax and test_xml_etree now return results in the test_main() function. Changes: * Rewrite TestResult as a dataclass with a new State class. * Add test.support.TestStats class and Regrtest.stats_dict attribute. * libregrtest.runtest functions now modify a TestResult instance in-place. * libregrtest summary lists the number of run tests and skipped tests, and denied resources. * Add TestResult.has_meaningful_duration() method. * Compute TestResult duration in the upper function. * Use time.perf_counter() instead of time.monotonic(). * Regrtest: rename 'resource_denieds' attribute to 'resource_denied'. * Rename CHILD_ERROR to MULTIPROCESSING_ERROR. * Use match/case syntadx to have different code depending on the test state. Notes on the backport: doctest.TestResults.skipped is a new feature in Python 3.13, so don't use it in the backport. Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com> (cherry picked from commit d4e534c)