perf: remove unnecessary string clone in maybe_concat_string_literal (apache#2173)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: andygrove

src/parser/mod.rs

@@ -11298,7 +11298,7 @@ impl<'a> Parser<'a> {
             while let Token::SingleQuotedString(ref s) | Token::DoubleQuotedString(ref s) =
                 self.peek_token_ref().token
             {
-                str.push_str(s.clone().as_str());
+                str.push_str(s);
                 self.advance_token();
             }
         }