Various improvements

context: fix memory free
subscribe: implement dummy methods
introspect: implement more
stream: keep track of dequeued buffers ourselves because we need to
be able to cancel and keep track of writable size.

src/meson.build

@@ -7,6 +7,7 @@ pipewire_pulseaudio_sources = [
   'error.c',
   'ext-device-manager.c',
   'ext-device-restore.c',
+  'ext-stream-restore.c',
   'format.c',
   'introspect.c',
   'json.c',
@@ -20,6 +21,8 @@ pipewire_pulseaudio_sources = [
   'stream.c',
   'strbuf.c',
   'subscribe.c',
+  'thread-mainloop.c',
+  'timeval.c',
   'utf8.c',
   'util.c',
   'version.c',