⚡ Bolt: Zero-allocation string evaluation for DelimTokenType and expected matching

Refactored `DelimTokenType` and `Tokenizer` logic to eliminate redundant `String` allocations during token identification and checking.

- Introduced `as_str()` returning `&'static str` for `DelimTokenType` variants.
- Refactored `check_op` and `fmt::Display` to use `as_str()` instead of `string()`.
- Refactored `Tokenizer::expect` to use `as_str()` without changing its token consumption semantics.
- Added tests to preserve `check_op` and `Tokenizer::expect` coverage.

Co-authored-by: ashyanSpada <22587148+ashyanSpada@users.noreply.github.com>

Author: google-labs-jules[bot]

src/token.rs

@@ -53,7 +53,6 @@ impl From<&str> for DelimTokenType {
 
 impl DelimTokenType {
     // ⚡ Bolt Optimization: Use `&'static str` to prevent heap allocation during string comparison.
-    #[cfg(not(tarpaulin_include))]
     pub fn as_str(&self) -> &'static str {
         use DelimTokenType::*;
         match self {
@@ -67,7 +66,6 @@ impl DelimTokenType {
         }
     }
 
-    #[cfg(not(tarpaulin_include))]
     pub fn string(&self) -> String {
         self.as_str().to_string()
     }
@@ -281,6 +279,20 @@ mod tests {
         assert_eq!(input.is_open_bracket(), output)
     }
 
+    #[test]
+    fn test_delim_token_type_as_str() {
+        assert_eq!(DelimTokenType::OpenParen.as_str(), "(");
+        assert_eq!(DelimTokenType::CloseParen.as_str(), ")");
+        assert_eq!(DelimTokenType::OpenBracket.as_str(), "[");
+        assert_eq!(DelimTokenType::CloseBracket.as_str(), "]");
+        assert_eq!(DelimTokenType::OpenBrace.as_str(), "{");
+        assert_eq!(DelimTokenType::CloseBrace.as_str(), "}");
+        assert_eq!(DelimTokenType::Unknown.as_str(), "??");
+
+        assert_eq!(DelimTokenType::OpenParen.string(), "(");
+        assert_eq!(DelimTokenType::Unknown.string(), "??");
+    }
+
     #[test]
     fn test_check_op() {
         use super::check_op;