docs(_ext[sphinx_pytest_fixtures]): suppress generic resource usage snippets

why: def test_example(server: Server): ... is trivially obvious to any
pytest user and adds nothing beyond the fixture signature. Override-hook
and factory snippets are genuinely useful (conftest.py pattern and
two-step instantiation pattern).

what:
- Return None for resource kind in _build_usage_snippet() instead of
  generating a generic test function snippet
- Keep autouse note, factory snippet, and override-hook snippet

Author: tony

docs/_ext/sphinx_pytest_fixtures.py

@@ -982,9 +982,10 @@ def _build_usage_snippet(
             "    assert obj is not None\n"
         )
     else:
-        sig_str = f"{fixture_name}: {ret_type}" if ret_type else fixture_name
-        fn_keyword = "async def" if is_async else "def"
-        code = f"{fn_keyword} test_example({sig_str}) -> None:\n    ...\n"
+        # Resource fixtures — generic snippet like
+        # ``def test_example(server: Server): ...`` is trivially obvious
+        # to any pytest user and adds nothing beyond the signature.
+        return None
 
     return nodes.literal_block(code, code, language="python")