add copyright and fix tests

Author: David Motsonashvili

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/GenerativeModel.kt

@@ -55,7 +55,7 @@ internal constructor(
   private val tools: List<Tool>? = null,
   private val toolConfig: ToolConfig? = null,
   private val systemInstruction: Content? = null,
-  private val generativeBackend: GenerativeBackend,
+  private val generativeBackend: GenerativeBackend = GenerativeBackend.VERTEX_AI,
   private val controller: APIController,
 ) {
   internal constructor(

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/GenerativeBackend.kt

@@ -1,3 +1,19 @@
+/*
+ * Copyright 2025 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
 package com.google.firebase.vertexai.type
 
 public enum class GenerativeBackend {