interfaces: improve remote API

Add return values to events and method callbacks. This makes it
possible to pass any error or async return value.
Add sync/done/error in both directions so that both proxy and resource
and perform/reply sync and produce errors.
Return a SPA_ASYNC from remote method calls (and events), keep the
sequence number in the connection.
With the core sync/done we can remove the client-node done method and
it's internal sequence number along with the seq number in method calls.
We can also use the method/event async return value to perform a sync
with as the unique sequence number for this method.
Add sync method and done/error event to proxy and resource.

spa/tools/spa-inspect.c

@@ -136,7 +136,7 @@ inspect_port_params(struct data *data, struct spa_node *node,
 	}
 }
 
-static void node_info(void *_data, const struct spa_node_info *info)
+static int node_info(void *_data, const struct spa_node_info *info)
 {
 	struct data *data = _data;
 
@@ -148,9 +148,10 @@ static void node_info(void *_data, const struct spa_node_info *info)
 		spa_debug_dict(2, info->props);
 	}
 	inspect_node_params(data, data->node);
+	return 0;
 }
 
-static void node_port_info(void *_data, enum spa_direction direction, uint32_t id,
+static int node_port_info(void *_data, enum spa_direction direction, uint32_t id,
 		const struct spa_port_info *info)
 {
 	struct data *data = _data;
@@ -164,6 +165,7 @@ static void node_port_info(void *_data, enum spa_direction direction, uint32_t i
 				id);
 		inspect_port_params(data, data->node, direction, id);
 	}
+	return 0;
 }
 
 static const struct spa_node_callbacks node_callbacks =

spa/tools/spa-monitor.c

@@ -61,12 +61,13 @@ static void inspect_item(struct data *data, struct spa_pod *item)
 	spa_debug_pod(0, NULL, item);
 }
 
-static void on_monitor_info(void *_data, const struct spa_dict *info)
+static int on_monitor_info(void *_data, const struct spa_dict *info)
 {
 	spa_debug_dict(0, info);
+	return 0;
 }
 
-static void on_monitor_event(void *_data, struct spa_event *event)
+static int on_monitor_event(void *_data, struct spa_event *event)
 {
 	struct data *data = _data;
 
@@ -84,6 +85,7 @@ static void on_monitor_event(void *_data, struct spa_event *event)
 		inspect_item(data, SPA_POD_CONTENTS(struct spa_event, event));
 		break;
 	}
+	return 0;
 }
 
 static int do_add_source(struct spa_loop *loop, struct spa_source *source)