fix improve enum error suggestion #3128

[asukaminato0721]

Summary

Fixes #3128

The change teaches call-argument diagnostics to suggest an enum member when the provided raw literal exactly matches a single expected enum value.

Test Plan

add test

[Copilot]

Pull request overview

Adds enum-member “did you mean …” suggestions to call-argument type mismatch diagnostics when a provided literal exactly matches an enum’s underlying value (fixing #3128).

Changes:

• Add enum-value → enum-member suggestion helper in enum handling code.
• Extend call-argument type-check error reporting to append an enum-member suggestion line when applicable.
• Add a regression test covering StrEnum argument mismatch suggestions.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
pyrefly/lib/test/enums.rs	Adds regression test asserting the new call-argument suggestion text for StrEnum.
pyrefly/lib/alt/class/enums.rs	Implements logic to map a raw literal type to a unique enum member suggestion.
pyrefly/lib/alt/answers_solver.rs	Injects enum-member suggestion lines into call-argument diagnostics during check_type failures.

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[rchen152]

The Copilot feedback looks legitimate here - specifically, the concerns about union handling and code duplication.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅