refactor: replace sequenceOf() with emptySequence() for clarity

lib/src/main/kotlin/org/example/RegexItem.kt

@@ -58,7 +58,7 @@ class AndThenItem(val left: RegexItem, val right: RegexItem) : RegexItem {
                 }
               } else {
                 // If right match fails, return an empty sequence
-                sequenceOf()
+                emptySequence()
               }
             }
     )