Simplify the stream API. make just 2 methods to queue and dequeue
buffers. Make just one callback when new buffers can be dequeued.
Add support for driver nodes such as the video-src.
Pass a pw_buffer structure to add/remove_buffer and make it possible
to attach metadata to it. This makes it a lot easier to implement
the gstreamer pipewire pool.
Call the stream process function from the main loop and use a lockfree
ringbuffer to pass buffers between the threads. Make it possible to
also call process from the RT thread.
unmap the buffer data when needed.
