It Flatten

seq1 := func(yield func(int) bool) {
    yield(1)
    yield(2)
}
seq2 := func(yield func(int) bool) {
    yield(3)
    yield(4)
}

flattened := it.Flatten([]iter.Seq[int]{seq1, seq2})
var result []int
for item := range flattened {
    result = append(result, item)
}
// result contains [1, 2, 3, 4]