Add types and code generation for event stream operation signatures

[JordonPhillips]

This adds in the interfaces for event streams and updates code generation to use them.

Example generated operation:

async def stream_messages(
    self,
    input: StreamMessagesInput,
    plugins: list[Plugin] | None = None,
) -> EventStream[
    InputEventStream[MessageStream],
    OutputEventStream[MessageStream],
    StreamMessagesOutput,
]:
    raise NotImplementedError()

These were part of separate prs that included http context, which has been removed. Doc strings have also been majorly beefed up. Example useage from the beefed up docs:

async def main():
    client = ChatClient()
    input = StreamMessagesInput(chat_room="aws-python-sdk", username="hunter7")

    async with client.stream_messages(input=input) as stream:
        stream.input_stream.send(MessageStreamMessage("Chat logger starting up."))
        response_handler = handle_output(stream)
        stream.input_stream.send(MessageStreamMessage("Chat logger active."))
        await response_handler

    async def handle_output(stream: EventStream) -> None:
        _, output_stream = await stream.await_output()
        async for event in output_stream:
            match event:
                case MessageStreamMessage():
                    print(event.value)
                case MessageStreamShutdown():
                    return
                case _:
                    stream.input_stream.send(
                        MessageStreamMessage("Unknown message type received. Shutting down.")
                    )
                    return

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[JordonPhillips]

I also had to add suppressions for new protocol tests that assert http-binding behaviors. We'll be re-writing all that binding code soon, so there's little value in fixing it now.

[JordonPhillips]

I split the suppressions out into another pr since it was blocking everything

[nateprewitt]

Couple typos, otherwise looks good.

[JordonPhillips]

No idea why codecov ate it

[nateprewitt]

Looks like a transient 503 for CodeCov, succeeded on retry.