Ensure a Callback and only one is provided in the Plugin. Also reduce boilerplate code in Nodes.

libraries/architecture/src/main/kotlin/io/element/android/libraries/architecture/NodeCallback.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2023, 2024 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+package io.element.android.libraries.architecture
+
+import com.bumble.appyx.core.node.Node
+import com.bumble.appyx.core.plugin.Plugin
+import com.bumble.appyx.core.plugin.plugins
+
+inline fun <reified I : Plugin> Node.callback(): I {
+    return requireNotNull(plugins<I>().singleOrNull()) { "Make sure to actually pass a Callback plugin to your node" }
+}