Fix blocking receiver sleeping after every read

[jprochazk]

Currently, the ws_receiver_blocking function would always sleep after every read. Additionally, it did not use the value from options.delay_blocking for the sleep delay. This would result in that thread being blocked for 10ms after every read no matter what the user configured it to, meaning it would receive data at an unnecessarily slow rate.

In this PR:

• Instead of using set_nonblocking or calling std::thread::sleep after every read, we now use set_read_timeout in the non-tokio native impls.
• The delay_blocking option is removed in favor of read_timeout
• The default for read_timeout is Some(10ms)
  • The ideal thing to do here would be to not block at all and instead use native polling APIs. This work is left as a TODO for another PR.
  • Use polling instead of thread::sleep #49

[emilk]

Nice find!

But I actually think there is an even better fix we can do.

Guided by this comment:

If we replace our calls to set_nonblocking with TcpStream::set_read_timeout(Duration::from_millis(10)) (or whatever) then socket.read would block waiting for message, and then error with Error::Io and e.kind() == std::io::ErrorKind::WouldBlock (which we can then ignore)

[jprochazk]

There's no call to set_nonblocking in the receiver impl, it just blocks. I would much rather jump ahead and switch it to polling if the bandaid here isn't good enough 😄

[jprochazk]

I ended up just going with set_read_timeout after all, at least for the time being, because using polling would introduce unsafe code into the project.

[emilk]

Beautiful! LGTM if tested