use proxies to nn.Module in dynamo generated GraphModules (#120756)

Summary:
Fixes remaining refleaks found when debugging pytorch/pytorch#119607, tests added in pytorch/pytorch#120657.

Also fixes some tests that xfail: pytorch/pytorch#120631 (not entirely sure why), but introduced tests now fail.

X-link: pytorch/pytorch#120756
Approved by: https://github.com/jansel

Reviewed By: huydhn

Differential Revision: D55225127

Pulled By: williamwen42

fbshipit-source-id: 0d402deb4246d981304985761b94f637970fabce

userbenchmark/dynamo/dynamobench/_dynamo/utils.py

@@ -2575,3 +2575,18 @@ class Invalid(dict):  # type: ignore[type-arg]
         pass
 
     return RemovableHandle(Invalid())
+
+
+# Returns a "proxy" (new object with the same class and dict) for (non-GraphModule) nn.Module's.
+# Attribute changes to the original object/proxy will be reflected in the other.
+# This is useful for cases where we want a keep-alive reference to a module without increasing
+# its reference count.
+def nn_module_proxy(mod):
+    if not isinstance(mod, torch.nn.Module):
+        return mod
+    if isinstance(mod, torch.fx.GraphModule):
+        # Dynamo-generated GM's shouldn't contain user-created GM's
+        return mod
+    proxy = mod.__class__.__new__(mod.__class__)
+    proxy.__dict__ = mod.__dict__
+    return proxy