feat(builtin): add Iter2::concat()

builtin/iter2.mbt

@@ -88,3 +88,37 @@ pub fn Iter2::to_array[A, B](self : Iter2[A, B]) -> Array[(A, B)] {
   }
   arr
 }
+
+///|
+/// Combines two iterators into one by appending the elements of the second iterator to the first.
+///
+/// # Arguments
+///
+/// * `self` - The first input iterator.
+/// * `other` - The second input iterator to be appended to the first.
+///
+/// # Returns
+///
+/// Returns a new iterator that contains the elements of `self` followed by the elements of `other`.
+///
+/// # Examples
+///
+/// ```moonbit
+/// test "Iter2::concat" {
+///   let ns = [10, 11, 12, 13, 14]
+///   let ms = [15, 16, 17, 18, 19]
+///   inspect!(
+///     ns.iter2().concat(ms.iter2()).to_array(),
+///     content="[(0, 10), (1, 11), (2, 12), (3, 13), (4, 14), (0, 15), (1, 16), (2, 17), (3, 18), (4, 19)]",
+///   )
+/// }
+/// ```
+pub fn Iter2::concat[A, B](
+  self : Iter2[A, B],
+  other : Iter2[A, B]
+) -> Iter2[A, B] {
+  fn(yield_) {
+    guard self.run(yield_) == IterContinue else { IterEnd }
+    other.run(yield_)
+  }
+}