Port for streaming HTTP transport.

Unlike the regular Transport port which returns complete responses, this port returns StreamResponse with an enumerable body for handling SSE (Server-Sent Events) and other streaming responses.

Implementation Requirements

Adapters implementing this behaviour should:

1. Make an HTTP request with appropriate streaming headers
2. Return a StreamResponse with an enumerable that yields events
3. Handle connection lifecycle (cleanup on enumeration completion)
4. Parse SSE events if content-type is text/event-stream

Example Adapter

defmodule MyStreamAdapter do
  @behaviour Pristine.Ports.StreamTransport

  @impl true
  def stream(%Request{} = request, %Context{} = context) do
    # Make streaming HTTP request
    # Parse SSE events
    # Return StreamResponse
    {:ok, %StreamResponse{stream: events, status: 200, headers: headers}}
  end
end