Add configurable sequence numbering command

internal/sequence/format.go

@@ -0,0 +1,20 @@
+package sequence
+
+import (
+	"fmt"
+	"strconv"
+)
+
+// formatNumber zero-pads the provided value using the requested width and returns
+// both the padded number string and the width that was ultimately used.
+func formatNumber(value, requestedWidth int) (string, int) {
+	if value < 0 {
+		value = 0
+	}
+	digitCount := len(strconv.Itoa(value))
+	width := requestedWidth
+	if width <= 0 || width < digitCount {
+		width = digitCount
+	}
+	return fmt.Sprintf("%0*d", width, value), width
+}