Return early from WithPadding when there is nothing to pad to

A caller that asks for a padding of zero gets its string back unchanged,
but only after WithPadding has measured it, and measuring means a
Decolorise lookup and a width scan over the result. A later commit pads
four cells of every commit in the list, and asks for a padding of zero
for all four whenever no rebase or bisect is in progress and the date
column is hidden, so make that case cost nothing.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

pkg/utils/formatting.go

@@ -36,6 +36,12 @@ func StringWidth(s string) int {
 
 // WithPadding pads a string as much as you want
 func WithPadding(str string, padding int, alignment Alignment) string {
+	if padding <= 0 {
+		// Nothing to pad to, and measuring the string isn't free: Decolorise
+		// compiles a regex whenever it is called with a string it hasn't cached.
+		return str
+	}
+
 	uncoloredStr := Decolorise(str)
 	width := StringWidth(uncoloredStr)
 	if padding < width {