FlatMap
func FlatMap[T any, R any](input *Channel[T], mapper func(T) *Channel[R], opts ...options.FlatMapOption) *Channel[R]
FlatMap transforms every input value into a Channel and for each of those, it sends all values to the output channel.
Example
output := FlatMap(input, func(i int) *Channel[int] { return FromSlice([]int{i, i * 10}) })
