[ty] Treat generator-expression exceptions as eagerly evaluated (#27735)
## Summary
Previously, generator expressions were assumed to execute eagerly for
name resolution and assignment expressions, but lazily when determining
whether exceptions could reach surrounding handlers:
```python
def may_raise() -> None: ...
caught = False
try:
((value := 1, may_raise()) for _ in [0])
except Exception:
caught = True
reveal_type(value) # int
reveal_type(caught) # Previously: Literal[False]; now: bool
```
We now apply the same eager-execution assumption to exception flow,
allowing potentially raising operations inside generator expressions to
reach enclosing exception handlers. Generator expressions now follow the
existing exception-flow behavior of list, set, and dictionary
comprehensions.
ruff
a46f553d - [ty] Treat generator-expression exceptions as eagerly evaluated (#27735)
