by using G_TYPE_NONE (== 1), we can pass this in the log handler
to point out the fact that we expected something but it's null

As a bonus, a null object always gets printed in red because that's
the first color in object_colors

Disconnecting core finishes all pending tasks, which is needed in order to avoid
possible leaks if some tasks are still pending when exiting.

+ use a more correct naming scheme to match the one from Spa
+ remove the default video source, since we now use a different
 session for video

This makes WIREPLUMBER_DEBUG behave just like PIPEWIRE_DEBUG.
Same levels, same syntax, easier for users.

ERROR & CRITICAL are always printed, as they should; there is no point
in disabling them, since:
- ERRORs are always fatal and should never ever happen
- CRITICALs are assertion failures and indicate bugs that need to be fixed