+ enable the new log writer on the executables
+ enable structured logging in the tests

This is an asynchronous operation class, like GTask,
but it is made to execute several operations underneath,
using a state machine, instead of just a single operation.

heavily based on the WpSession implementation

This also adds a "test server" helper, which is used to
start a local pipewire server in the same process, for testing
functionality that requires a server.