style: use poll loop for CallState

[mattsse]

transforms the separate CallState::poll_ functions into a single poll loop.

this effectively replaces a waker call with a loop so the response is polled (started) right await without going through the scheduler

[prestwich]

the other idiom i've been moving towards is an explicit continuation:

alloy/crates/provider/src/provider/call.rs

Lines 88 to 90 in 5940871

	*self = Self::Running(fut);
	self.poll_running(cx)
	}

[mattsse]

this also works, but this becomes more tricky if the state machine is >2 states or has more complex transitions