API: Type mapping

[AldaronLau]

Allocation Reduction

Should be able to create a custom struct that contains a whisk::Channel and constructs as Arc<Self> containing the channel (but not within another Arc).

#[derive(Clone)]
struct MyChannelWrapper<T, U> {
   data: T,
   channel: whisk::Channel<U>,
}

impl<T, U> MyChannelWrapper<T, U> {
    fn new() -> Arc<Self> { ... }
}