Fix unpickling errors for Standard Library modules

[leogama]

I'll try to fix errors preventing Standard Library modules pickled by dill.dump_module() from unpickling.

Commits:

1. Save enums by reference while Support ABC and Enums #450 is not ready — half of the StdLib modules that fail to unpickle in Python 3.11 fail because of this: ast, enum, http, inspect, plistlib, pstats, py_compile, signal, socket, ssl