Consider making `Client` `Send + Sync`

[bobertoyin]

Is your feature request related to a problem? Please describe.
The Client struct doesn't mutate itself, so it should be handy enough to add these traits to the client in order to make it work better with multi-threaded use-cases.

Describe the solution you'd like
Derive/implement the above traits for the struct.

Describe alternatives you've considered
N/A

Additional context
N/A

[bobertoyin]

This is silly, I am silly, ignore