[red-knot] Emit a diagnostic if the value of a starred expression or a yield from expression is not iterable

[AlexWaygood]

Summary

This PR builds on #13195. It ensures that we emit the not-iterable diagnostic on expressions such as the following:

class NotIterable: pass

def foo():
    [*NotIterable()]
    yield from NotIterable()

The Type::iterate() method is refactored slightly so that it's easier for callers of the method to all emit the same diagnostic: it now accepts a diagnostic_fn callback that emits a diagnostic if the type is not found to be an iterable type.

I deliberately haven't tackled comprehensions in this PR, for two reasons:

1. There's some more complications there
2. I think @dhruvmanila has been working a lot on comprehensions/there are several TODOs in the code that are assigned to him!

Test Plan

cargo test

[codspeed-hq]

CodSpeed Performance Report

Merging #13240 will not alter performance

_{Comparing alex/redknot-iterables (53cc0a2) with main (46a4573)}

Summary

✅ 32 untouched benchmarks

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[carljm]

I don't much like the callback or the new iteration-specific returned enum. What I would prefer is a more general inference-context object that gets passed into all inference methods on Type and has the ability to emit a diagnostic. Then iterate itself can emit a consistent diagnostic.