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.

[ev-br]

I've to admit this looks a bit overboard. If the problem is that None in dtype_to_name fails with mlx.core, would the following do the trick? cc @aaishwarymishra --- would it fix the problem you were having:

$ git diff
diff --git a/reporting.py b/reporting.py
index 579aa21..0dcf410 100644
--- a/reporting.py
+++ b/reporting.py
@@ -17,6 +17,8 @@ except ImportError:
     raise ImportError("pytest-json-report is required to run the array API tests")
 
 def to_json_serializable(o):
+    if o is None:
+        return o
     if o in dtype_to_name:
         return dtype_to_name[o]
     if isinstance(o, (BuiltinFunctionType, FunctionType, type)):

[ev-br]

Actually, scratch that. Need some more coffee, sorry. Now that I re-read the function itself, my diff above is the same fix.
LGTM, thanks @tomatotomata

[aaishwarymishra]

@ev-br happens to the best of us 😭