fix add quickfix for Unnecessary str() call; #3342

[asukaminato0721]

Summary

Fixes #3342

Added a local quick fix for UnnecessaryTypeConversion diagnostics so str(x) on an already-str value now offers Remove unnecessary str() call and rewrites it to x.

Test Plan

add test

[Copilot]

Pull request overview

Adds a local LSP quick fix for the UnnecessaryTypeConversion diagnostic so redundant conversion calls like str(x) (when x is already str) offer an actionable code action that rewrites the call to just x (Fixes #3342).

Changes:

• Added a new quick-fix implementation that replaces an unnecessary builtin conversion call with its sole argument (with parenthesization when needed).
• Wired the quick fix into the LSP code-action pipeline for ErrorKind::UnnecessaryTypeConversion.
• Added an LSP golden-style test that validates the new code action behavior for str(x).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
pyrefly/lib/test/lsp/code_actions.rs	Adds a regression test asserting the new “Remove unnecessary str() call” code action and edit output.
pyrefly/lib/state/lsp/quick_fixes/unnecessary_type_conversion.rs	Implements the quick fix that identifies the enclosing call and replaces it with the argument expression (wrapping when necessary).
pyrefly/lib/state/lsp/quick_fixes/mod.rs	Exposes the new unnecessary_type_conversion quick-fix module.
pyrefly/lib/state/lsp.rs	Registers the new quick fix for ErrorKind::UnnecessaryTypeConversion when building local code actions.

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[github-actions]

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