Test run errors are surfaced as run/target-level errors instead of synthetic test cases

xctest runner failures that previously appeared as synthetic “xctest () encountered an error” test cases are now shown in a dedicated Errors section on the test run page. This keeps them out of the failed test count, prevents unbounded test_case.created webhook notifications, and aligns the dashboard with Xcode. The run page’s Failures section is also renamed to Test Failures to make the distinction clear.