[ty] infer `name` and `value` for enum members (#20311)
## summary
- this pr implements the following attributes for `Enum` members:
- `name`
- `_name_`
- `value`
- `_value_`
- adds a TODO test for `my_enum_class_instance.name`
- only implements if the instance is a subclass of `Enum` re: this
[comment](https://github.com/astral-sh/ruff/pull/19481#issuecomment-3103460307)
and existing
[test](https://github.com/thejchap/ruff/blob/c34449ed7ca4b043d514240e212335a2554d0fb1/crates/ty_python_semantic/resources/mdtest/enums.md?plain=1#L625)
### pointers
- https://github.com/astral-sh/ty/issues/876
- https://typing.python.org/en/latest/spec/enums.html#enum-definition
- https://github.com/astral-sh/ruff/pull/19481#issuecomment-3103460307
## test plan
- mdtests
- triaged conformance diffs here:
https://diffswarm.dev/d-01k531ag4nee3xmdeq4f3j66pb
- triaged mypy primer diffs here for django-stubs:
https://diffswarm.dev/d-01k5331n13k9yx8tvnxnkeawp3
- added a TODO test for overriding `.value`
- discord diff seems reasonable
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Co-authored-by: David Peter <mail@david-peter.de>
