Add an explicit fast path for whitespace to is_identifier_continuation (#9532)

crates/ruff_python_trivia/src/tokenizer.rs

@@ -136,6 +136,8 @@ fn is_identifier_start(c: char) -> bool {
 // Checks if the character c is a valid continuation character as described
 // in https://docs.python.org/3/reference/lexical_analysis.html#identifiers
 fn is_identifier_continuation(c: char) -> bool {
+    // Arrange things such that ASCII codepoints never
+    // result in the slower `is_xid_continue` getting called.
     if c.is_ascii() {
         matches!(c, 'a'..='z' | 'A'..='Z' | '_' | '0'..='9')
     } else {