fix: avoid dtype comparison for None report metadata

[tomatotomata]

Summary

• avoid comparing None with array-library dtype objects before looking them up in dtype_to_name
• add a regression test using an MLX-like dtype whose equality operation rejects None

Closes #447

Validation

• ARRAY_API_TESTS_MODULE=numpy PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 python -m pytest -q -p pytest_jsonreport.plugin meta_tests/test_reporting.py passed: 1 test
• ARRAY_API_TESTS_MODULE=numpy PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 python -m pytest -q -p pytest_jsonreport.plugin meta_tests/test_utils.py passed: 30 tests
• python -m compileall -q reporting.py meta_tests/test_reporting.py passed
• git diff --check passed

The full suite was not run. The focused commands disable unrelated globally installed pytest plugins and load the repository's JSON-report plugin explicitly.