implement `Send` + `Sync` for `ServiceBusReceiver` and `ServiceBusReceiver`

[Zizico2]

Any chance ServiceBusSender and ServiceBusReceiver could be Sync? Or should we just Arc<Mutex<>> it? feels weird since there are already some Arcs internally and I think this is a common enough requirement that the crate could support it (?). I could try to tackle this if it makes sense

[Zizico2]

And Clone while where at it

[minghuaw]

Any chance ServiceBusSender and ServiceBusReceiver could be Sync?

I don't think so. The internal AMQP receiver needs to modify some states when receiving messages, and this ultimately comes to tokio::sync::mpsc::Receiver which takes a &mut self for the recv() method (https://docs.rs/tokio/latest/tokio/sync/mpsc/struct.Receiver.html#method.recv).

Of course I could have use an Arc<Mutex<>> internally, but that's hiding too much details of a potentially costly operation from the user.

[minghuaw]

@Zizico2 I am going to close this issue if there is no follow-up questions.

[Zizico2]

Yep. Go ahead