The value of enums should be unstructured and structured too

[reversefold]

I'm running into an interesting issue where the value of an enum is a structured value which isn't being properly unstructured and that's causing issues with serialization.

Here's a simple example:

import attrs
import cattrs
import enum

class E(enum.Enum):
    A = 0
    B = 1

class EE(enum.Enum):
    A0 = (E.A, 0)
    A1 = (E.A, 1)
    B0 = (E.B, 0)
    B1 = (E.B, 1)

@attrs.define
class C:
    e: E
    ee: EE

c = C(e=E.B, ee=EE.A1)
print(cattrs.unstructure(c))

The e attribute of the C class is properly unstructured to a 1 value and the ee attribute is unstructured to the tuple (E.A, 1), but the E.A in that resulting tuple is not unstructured, which causes, for instance, JSON serialization to fail.