Work around PyQt memory leak on the Krita::documents() method.

ai_diffusion/document.py

@@ -237,7 +237,18 @@ def current_time(self):
 
     @property
     def is_valid(self):
-        return self._doc in Krita.instance().documents()
+        # workaround 144MB/document/day pykrita memory leak (experimentally determined).
+        # `documents()` returns a `QList<Document*>`. The QList is cleaned up, but SIP
+        # doesn't know what to make of the pointers and just leaks them.
+        # If Krita ever fixes the documents() method, this will cause a double-delete and
+        # start crashing. So if you're seeing crashes on a new version, this is a good
+        # candidate.
+        # return self._doc in Krita.instance().documents()
+        documents = Krita.instance().documents()
+        result = self._doc in documents
+        for document in documents:
+            document.deleteLater()
+        return result
 
     @property
     def is_active(self):