createTogetherProvider function
Create an OpenAI provider for Together AI
Implementation
OpenAIProvider createTogetherProvider({
  required String apiKey,
  String model = ProviderDefaults.togetherAIDefaultModel,
  double? temperature,
  int? maxTokens,
  String? systemPrompt,
}) {
  final config = OpenAIConfig(
    apiKey: apiKey,
    model: model,
    baseUrl: ProviderDefaults.togetherAIBaseUrl,
    temperature: temperature,
    maxTokens: maxTokens,
    systemPrompt: systemPrompt,
  );
  return OpenAIProvider(config);
}