This serves as a base class for daemon plugins, which are implemented
inside modules

And also provide a way to disable this integration at runtime to
get pipewire's log back, with WIREPLUMBER_NO_PW_LOG=1

The GLib error level is fatal, but pipewire doesn't use it that way.
Also, the GLib critical level is meant only for programming errors
(assertions) and not for runtime errors. warn & msg levels really
fit well with the error & warn, as they are being used in pipewire
currently.

This is mostly useful when using the adapter with audiotestsrc,
which supports an infinite number of channels. By specifying
a preference, we can limit it to the number of channels that we want.

It is a valid use case to do things like call wp_session_item_export()
from within the async ready callback of _activate(), and it's not
possible unless the ACTIVATING flag has been cleared first.

To do this, use a GCClosure to wrap the callback and install marshal
guards, which are called before and after the callback, to modify
the flags.

This aligns better with the general design of consuming property
objects on constructors, both in PipeWire and WirePlumber APIs

* there is just one link, no need for a list
* warn if something goes wrong and don't assert

It can be a bit tricky because the "installed" signal may be fired
from inside the context of wp_core_install_object_manager(),
in which case the main loop should not be executed (or it will never quit)

We can now call wp_proxy_request_destroy() on endpoint links and
the WpImplEndpointLink together with the session item that created
it will be cleaned up

When a pw_global is removed on the server (by pw_registry_destroy() or other
means), it triggers the proxy removed & the registry global_remove callbacks,
but it does not necessarily destroy the pw_proxy.

For client proxies, we were previously destroying them by unrefing the WpProxy
in wp_global_rm_flags(), since the global was not "owned" by the WpProxy.

For impl proxies, we were not doing anything, as we expected that it would
only be removed from the registry if the local WpProxy was destroyed first.
This is not always the case, though, as the server or another client may
request to destroy this proxy with pw_registry_destroy()

Now we always destroy the pw_proxy as soon as it is removed from the registry,
no matter if it was a client or an impl proxy. If it was an impl proxy,
the WpProxy will continue to live and it's up to the code that created it
to handle the "pw-proxy-destroyed" signal and do something meaningful.
If it was a client proxy, the global will still unref the WpProxy right after
destroying the pw_proxy and there is no change in behavior.

Useful to destroy links and endpoint-links