feat: iterator.While, slimmed comments in saccharine

pkg/saccharine/scan.go

@@ -47,18 +47,7 @@ func scanToken(i *iterator.Iterator[rune]) (*Token, error) {
 		return token.New(TokenHardBreak, index), nil
 	case letter == '#':
 		// Skip everything until the next newline or EOF.
-		for !i.Done() {
-			r, err := i.Next()
-			if err != nil {
-				return nil, fmt.Errorf("error while parsing comment: %w", err)
-			}
-
-			if r == '\n' {
-				// Put the newline back so it can be processed as a soft break.
-				i.Back()
-				break
-			}
-		}
+		i.While(func(r rune) bool { return r != '\n' })
 		return nil, nil
 	case unicode.IsSpace(letter):
 		return nil, nil