Move defaultVertexAIAPIConfig to unit tests; unused in SDK

Author: andrewheard

FirebaseAI/Sources/FirebaseAI.swift

@@ -194,11 +194,6 @@ public final class FirebaseAI: Sendable {
   /// Lock to manage access to the `instances` array to avoid race conditions.
   private nonisolated(unsafe) static var instancesLock: os_unfair_lock = .init()
 
-  static let defaultVertexAIAPIConfig = APIConfig(
-    service: .vertexAI(endpoint: .firebaseProxyProd, location: "us-central1"),
-    version: .v1beta
-  )
-
   static func createInstance(app: FirebaseApp?,
                              apiConfig: APIConfig,
                              useLimitedUseAppCheckTokens: Bool) -> FirebaseAI {

FirebaseAI/Tests/Unit/TestUtilities/FirebaseAI+DefaultAPIConfig.swift

@@ -0,0 +1,22 @@
+// 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.
+
+@testable import FirebaseAI
+
+extension FirebaseAI {
+  static let defaultVertexAIAPIConfig = APIConfig(
+    service: .vertexAI(endpoint: .firebaseProxyProd, location: "us-central1"),
+    version: .v1beta
+  )
+}