Add binary request example

[heaths]

Also refactors FileStream from azure_core to typespec_client_core, plus some trait implementations on necessary request structures to make it all work.

[heaths]

I need to play around with this some. Track 1 didn't have a fully asynchronous answer either. I'm thinking the answer is to convert from a Body to RequestContent<T>, and add support for Stream into Body. We have a tokio-based FileStream already that I need to migrate to typespec_client_core (if necessary; might be outdated, actually).

Basically, it'd go:

let file_stream = FileStream::new(tokio::fs::File::open("data.bin")?);
let body: Body = file_stream.into();
client.put_data(&ctx, body, None).await?;

/cc @analogrelay @demoray @cataggar