fix(directives): Guard against duplicate deprecated CSS class on multi-fixture pages

why: transform_content() walks all desc nodes in the document and
appends spf-deprecated without checking if already present. On a page
with multiple deprecated fixtures, each call re-appends to every
already-matched parent.
what:
- Add membership check before appending _CSS.DEPRECATED to parent classes

Author: tony

packages/sphinx-autodoc-pytest-fixtures/src/sphinx_autodoc_pytest_fixtures/_directives.py

@@ -298,7 +298,8 @@ def transform_content(
             for parent in self.state.document.findall(addnodes.desc):
                 for sig in parent.findall(addnodes.desc_signature):
                     if sig.get("spf_deprecated"):
-                        parent["classes"].append(_CSS.DEPRECATED)
+                        if _CSS.DEPRECATED not in parent["classes"]:
+                            parent["classes"].append(_CSS.DEPRECATED)
                         break
 
         # --- Lifecycle callouts (session note + override hook tip) ---