chore: minor improvement for comments

[alaningtrump]

minor improvement for comments

[cursor]

PR Summary

Low Risk
Comment-only edits with no runtime, API, or parsing logic impact.

Overview
Fixes two comment typos with no code or behavior changes.

In parser.rs, the expect_item_impl_inner doc comment now reads "or an impl alias" instead of "or and impl alias". In ast_test.rs, the setup helper comment now says "create" instead of "crate" when describing the SyntaxFile green-id hack.

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[reviewable-StarkWare]

This change is 

[orizi]

@orizi reviewed 2 files and all commit messages, and made 1 comment.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on alaningtrump).