[ty] Support iterating over enums (#19486)

## Summary

Infer the correct type in a scenario like this:

```py
class Color(Enum):
    RED = 1
    GREEN = 2
    BLUE = 3

for color in Color:
    reveal_type(color)  # revealed: Color
```

We should eventually support this out-of-the-box when
https://github.com/astral-sh/ty/issues/501 is implemented. For this
reason, @AlexWaygood would prefer to keep things as they are (we
currently infer `Unknown`, so false positives seem unlikely). But it
seemed relatively easy to support, so I'm opening this for discussion.

part of https://github.com/astral-sh/ty/issues/183

## Test Plan

Adapted existing test.

## Ecosystem analysis

```diff
- warning[unused-ignore-comment] rotkehlchen/chain/aggregator.py:591:82: Unused blanket `type: ignore` directive
```

This `unused-ignore-comment` goes away due to a new true positive.

crates/ty_python_semantic/resources/mdtest/enums.md

@@ -406,8 +406,7 @@ class Color(Enum):
     BLUE = 3
 
 for color in Color:
-    # TODO: Should be `Color`
-    reveal_type(color)  # revealed: Unknown
+    reveal_type(color)  # revealed: Color
 
 # TODO: Should be `list[Color]`
 reveal_type(list(Color))  # revealed: list[Unknown]