fix(ast-engine): restore Language::from_path regression tests

[Copilot]

Tests for Language::from_path panic behavior were removed in a prior cleanup commit (a79e527) and never restored, leaving the contract untested despite the implementation being correct.

Changes

• crates/ast-engine/src/language.rs
  • Restored NoFromPath and TsxWithFromPath test structs covering the un-overridden (panics) and overridden (returns Option) cases
  • Restored default_from_path_panics and overridden_from_path_does_not_panic tests
  • Extracted shared test helpers (tsx_kind_to_id, tsx_field_to_id, tsx_ts_language) to reduce duplication across test impls
  • Tightened from_path doc comment to explicitly document the panic-on-unimplemented contract

#[test]
#[should_panic(expected = "Language::from_path is not implemented for type")]
fn default_from_path_panics() {
    let _ = NoFromPath::from_path("some/file.rs");
}

#[test]
fn overridden_from_path_does_not_panic() {
    assert!(TsxWithFromPath::from_path("component.tsx").is_some());
    assert!(TsxWithFromPath::from_path("main.rs").is_none());
}

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[Copilot]

Pull request overview

Restores regression tests and clarifies the documented contract for Language::from_path in thread-ast-engine, ensuring the default “unimplemented” (panic) behavior and an overridden (non-panicking) implementation remain verified going forward.

Changes:

• Tightened Language::from_path rustdoc to explicitly document that the default implementation panics.
• Reintroduced tests covering both the default (panic) and overridden (returns Option) from_path behaviors.
• Extracted small shared TSX/tree-sitter helpers to reduce duplication across test language impls.

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[github-actions]

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