An enum used as another enum's value is not unstructured by the json converter

Trivial example:

import cattrs
import enum
import cattr.preconf.json

c = cattr.preconf.json.make_converter()
class TE(enum.Enum):
    A = 1
class TE2(enum.Enum):
    C = TE.A
print(repr(c.unstructure(TE2.C)))

Outputs:

<TE.A: 1>

Should output:

1

The actual use-case I have for this is an enum with a value that has a tuple with another enum's value and an additional integer value so it isn't quite this trivial. Nevertheless, the problem is the same. An enum's value may be one which needs to be recursively unstructured. In fact, the same issue arises if an attrs class instance is used as an enum's value:

import attrs
@attrs.define
class C:
    a: int
class EC(enum.Enum):
    D = C(1)
print(repr(c.unstructure(EC.D)))

The reverse issue also happens when trying to use structure on what the jsonable result should be:

c.structure({"a": 1}, EC)

c.structure(1, TE2)

Both fail.

Start by reproducing the examples through cattr.preconf.json.make_converter(), focusing on unstructure and structure for enums whose values are other enums or attrs instances. Done means nested enum values and attrs instances are recursively converted in both directions, including the tuple-valued case described in the issue.