Fix BidiGenerateContentClientMessage encoding

Author: andrewheard

FirebaseAI/Sources/Types/Internal/Live/BidiGenerateContentClientMessage.swift

@@ -15,7 +15,7 @@
 import Foundation
 
 /// Messages sent by the client in the BidiGenerateContent RPC call.
-enum BidiGenerateContentClientMessage: Encodable {
+enum BidiGenerateContentClientMessage {
   /// Message to be sent in the first and only first client message.
   case setup(BidiGenerateContentSetup)
 
@@ -28,3 +28,26 @@ enum BidiGenerateContentClientMessage: Encodable {
   /// Response to a `ToolCallMessage` received from the server.
   case toolResponse(BidiGenerateContentToolResponse)
 }
+
+extension BidiGenerateContentClientMessage: Encodable {
+  enum CodingKeys: CodingKey {
+    case setup
+    case clientContent
+    case realtimeInput
+    case toolResponse
+  }
+
+  func encode(to encoder: any Encoder) throws {
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    switch self {
+    case let .setup(setup):
+      try container.encode(setup, forKey: .setup)
+    case let .clientContent(clientContent):
+      try container.encode(clientContent, forKey: .clientContent)
+    case let .realtimeInput(realtimeInput):
+      try container.encode(realtimeInput, forKey: .realtimeInput)
+    case let .toolResponse(toolResponse):
+      try container.encode(toolResponse, forKey: .toolResponse)
+    }
+  }
+}