Allow for inheriting from proxy

The code is copied from https://github.com/GrahamDumpleton/wrapt/blob/5c0997c0b5be36da5f621c3473c95f9efe14891e/src/wrapt/wrappers.py#L136-L138

Author: Atry

src/lazy_object_proxy/simple.py

@@ -1,4 +1,5 @@
 import operator
+import sys
 
 from .compat import string_types
 from .compat import with_metaclass
@@ -257,3 +258,7 @@ def __reduce_ex__(self, protocol):
         from .utils import __await__
 
         __aiter__, __anext__, __await__, __aenter__, __aexit__  # noqa
+
+    if sys.hexversion >= 0x03070000:
+        def __mro_entries__(self, _):
+            return (self.__wrapped__,)