move contains to base command class so cluster can reuse it

(cherry picked from commit 18ff9a2)

Author: amirreza8002

django_valkey/base.py

@@ -158,6 +158,9 @@ def client(self) -> Client:
 
 @decorate_all_methods(omit_exception)
 class BackendCommands:
+    def __contains__(self, item):
+        return self.has_key(item)
+
     def set(self: BaseValkeyCache, *args, **kwargs) -> bool:
         return self.client.set(*args, **kwargs)
 

django_valkey/cache.py

@@ -6,6 +6,3 @@
 
 class ValkeyCache(BaseValkeyCache[DefaultClient, Valkey], BackendCommands):
     DEFAULT_CLIENT_CLASS = "django_valkey.client.DefaultClient"
-
-    def __contains__(self, item):
-        return self.has_key(item)