Move FakeNodeFactoriesBindings to the testutils module

The fake was declared in RootFlowNodeTest, so other tests could not use
it. Move it to the testutils module, in a new node package.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/testutils/src/main/kotlin/io/element/android/tests/testutils/node/FakeNodeFactoriesBindings.kt

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2026 Element Creations 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.tests.testutils.node
+
+import com.bumble.appyx.core.node.Node
+import io.element.android.libraries.architecture.AssistedNodeFactory
+import io.element.android.libraries.architecture.NodeFactoriesBindings
+import kotlin.reflect.KClass
+
+class FakeNodeFactoriesBindings(
+    private val nodeFactories: Map<KClass<out Node>, AssistedNodeFactory<*>>,
+) : NodeFactoriesBindings {
+    override fun nodeFactories() = nodeFactories
+}