perf(printf): optimize shell metacharacter lookup with O(1) lookup table

Replace linear search through SHELL_META_CHARS string with a const lookup
table for O(1) character classification. This improves performance for
the printf %q implementation without changing behavior.

- Add SHELL_META_LOOKUP static array initialized at compile time
- Add is_shell_meta() helper using the lookup table
- Remove unused SHELL_META_CHARS constant

Author: naoNao89

.vscode/cspell.dictionaries/jargon.wordlist.txt

@@ -84,6 +84,7 @@ lossily
 lstat
 mebi
 mebibytes
+metacharacter
 metacharacters
 mergeable
 microbenchmark

src/uucore/src/lib/features/quoting_style/printf_quoter.rs

@@ -14,26 +14,39 @@
 
 use super::Quoter;
 
-/// Characters that need escaping in shell context
+/// Lookup table for shell metacharacters (for O(1) lookup)
 /// Note: Tilde (~) is NOT escaped by bash printf %q
-const SHELL_META_CHARS: &str = " \t\n'\"\\`$&|;()<>[]{}*?!#";
+static SHELL_META_LOOKUP: [bool; 256] = const {
+    let mut lookup = [false; 256];
+    let meta = b" \t\n'\"\\`$&|;()<>[]{}*?!#";
+    let mut i = 0;
+    while i < meta.len() {
+        lookup[meta[i] as usize] = true;
+        i += 1;
+    }
+    lookup
+};
 
 /// Check if a byte is a control character
 #[inline]
 fn is_control(b: u8) -> bool {
     b < 0x20 || b == 0x7F
 }
 
+/// Check if a byte is a shell metacharacter
+#[inline]
+fn is_shell_meta(b: u8) -> bool {
+    SHELL_META_LOOKUP[b as usize]
+}
+
 /// Check if string contains any control characters
 fn has_control_chars(s: &[u8]) -> bool {
     s.iter().any(|&b| is_control(b))
 }
 
 /// Check if string needs any quoting at all
 fn needs_quoting(s: &[u8]) -> bool {
-    s.is_empty()
-        || s.iter()
-            .any(|&b| SHELL_META_CHARS.as_bytes().contains(&b) || is_control(b))
+    s.is_empty() || s.iter().any(|&b| is_shell_meta(b) || is_control(b))
 }
 
 pub(super) struct PrintfQuoter;
@@ -65,7 +78,7 @@ impl PrintfQuoter {
         let mut result = Vec::with_capacity(input.len() * 2);
 
         for &b in input {
-            if SHELL_META_CHARS.as_bytes().contains(&b) {
+            if is_shell_meta(b) {
                 result.push(b'\\');
             }
             result.push(b);