feat(rbs): Add highlight rules for inline annotations (#262)

## Summary

- Add missing highlight rules from upstream tree-sitter-rbs for RBS
inline annotations (`#:` and `# @rbs` comments)
- Highlights generic modifiers (`unchecked`, `out`, `in`), unnamed
parameters, inline keywords (`inherits`, `generic`, `override`, `skip`),
doc comments, and operators (`?`, `*`, `**`, `&`)
- All capture names follow existing conventions in the file

## Test plan

- [x] `cargo test` passes (60 tests, no changes to test fixtures)
- [x] Manually verify RBS inline annotation highlighting in Zed

Author: hakanensari

languages/rbs/highlights.scm

@@ -107,13 +107,22 @@
 
 (global_name) @variable
 
+; Generics Keywords
+[
+  (generics_unchecked)
+  (generics_variance)
+] @keyword
+
 ; Standard Arguments
 (parameter
   (var_name) @variable.parameter)
 
 ; Keyword Arguments
 (keyword) @variable.parameter
 
+; Unnamed Arguments
+(unnamed_parameter) @variable.parameter
+
 ; Self
 (self) @variable.builtin
 
@@ -145,6 +154,10 @@
   "&"
   "|"
   "^"
+  "?"
+  (rest_operator)
+  (block_operator)
+  (optional_block_operator)
 ] @operator
 
 ; Punctuation
@@ -164,3 +177,19 @@
 
 ; RBS Inline prefix (keep comment color)
 (inline_prefix) @comment
+
+; RBS Inline keywords
+(inline_class_annotation) @keyword
+
+(inline_generic) @keyword
+
+(inline_override) @keyword
+
+(inline_skip) @keyword
+
+; RBS Inline doc comment (-- description)
+(inline_doc_comment) @comment
+
+; RBS Inline doc param names (e.g. @rbs client_request_token: String)
+(inline_doc
+  (var_name) @variable.parameter)