rust: Restore and update attribute highlighting (#25501)

#25333 added broader highlighting for identifiers, which broke the
generic query for attribute queries, resulting in these being
highlighted the same as identifiers.

To accomodate for this change, this PR updates the attribute matches to
be more specific.

Additionally, path matches in scoped identifiers are no longer
highlighted as attributes, as seen in the comparison screenshot. Can
revert this if requested.

| Zed Preview | <img width="750" alt="preview"
src="https://github.com/user-attachments/assets/2cd2e830-f510-4adf-8ce9-c41ed6fb157c"
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| `main` | <img width="750" alt="main"
src="https://github.com/user-attachments/assets/cbe93186-9afd-4515-bc06-e519fd4ee6af"
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| This PR | <img width="750" alt="pr"
src="https://github.com/user-attachments/assets/68270de8-e083-4fc6-a45e-25d3151acd87"
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The generic match for `token_tree` is needed to recursively match
patterns like `#[cfg(any(test, feature = "test-support"))]` (or at least
I was unable to find a better query here). I tried to validate that this
does not break any other highlights and I believe it does not. However,
I might have still missed something.

Release Notes:

- N/A

crates/languages/src/rust/highlights.scm

@@ -190,5 +190,9 @@ operator: "/" @operator
 
 (parameter (identifier) @variable.parameter)
 
-(attribute_item) @attribute
-(inner_attribute_item) @attribute
+(attribute_item (attribute (identifier) @attribute))
+(inner_attribute_item (attribute (identifier) @attribute))
+; Match nested snake case identifiers in attribute items.
+(token_tree (identifier) @attribute (#match? @attribute "^[a-z\\d_]*$"))
+; Override the attribute match for paths in scoped identifiers.
+(token_tree (identifier) @variable "::")