ls: simplify canonicalize_indicator_value

Author: sylvestre

src/uu/ls/src/colors.rs

@@ -786,11 +786,8 @@ fn parse_indicator_codes() -> (FxHashMap<Indicator, String>, bool) {
 }
 
 fn canonicalize_indicator_value(value: &str) -> Cow<'_, str> {
-    if value.len() == 1 && value.chars().all(|c| c.is_ascii_digit()) {
-        let mut canonical = String::with_capacity(2);
-        canonical.push('0');
-        canonical.push_str(value);
-        Cow::Owned(canonical)
+    if value.len() == 1 && value.as_bytes()[0].is_ascii_digit() {
+        Cow::Owned(format!("0{value}"))
     } else {
         Cow::Borrowed(value)
     }