feat(chat-models): Support seed, system_fingerprint and JSON Mode in ChatOpenAI

[davidmigloz]

Seed example:

final prompt = PromptValue.string('How are you?');
final llm = ChatOpenAI(
  apiKey: openaiApiKey,
  temperature: 0,
  seed: 9999,
);
final res1 = await llm.invoke(prompt);
expect(res1.generations, hasLength(1));
final generation1 = res1.generations.first;
final res2 = await llm.invoke(prompt);
expect(res2.generations, hasLength(1));
final generation2 = res2.generations.first;
expect(
  res1.modelOutput?['system_fingerprint'],
  res2.modelOutput?['system_fingerprint'],
);
expect(generation1.output, generation2.output);

JSON mode example:

 final prompt = PromptValue.chat([
   ChatMessage.system(
     "Extract the 'name' and 'origin' of any companies mentioned in the "
     'following statement. Return a JSON list.',
   ),
   ChatMessage.human(
     'Google was founded in the USA, while Deepmind was founded in the UK',
   ),
 ]);
 final llm = ChatOpenAI(
   apiKey: openaiApiKey,
   model: 'gpt-4-1106-preview',
   temperature: 0,
   seed: 9999,
   responseFormat: const ChatOpenAIResponseFormat(
     type: ChatOpenAIResponseFormatType.jsonObject,
   ),
 );
 final res = await llm.invoke(prompt);
 expect(res.generations, hasLength(1));
 final outputMsg = res.generations.first.output;
 final outputJson = json.decode(outputMsg.content) as Map<String, dynamic>;
 expect(outputJson['companies'], isNotNull);
 final companies = outputJson['companies'] as List<dynamic>;
 expect(companies, hasLength(2));
 final firstCompany = companies.first as Map<String, dynamic>;
 expect(firstCompany['name'], 'Google');
 expect(firstCompany['origin'], 'USA');
 final secondCompany = companies.last as Map<String, dynamic>;
 expect(secondCompany['name'], 'Deepmind');
 expect(secondCompany['origin'], 'UK');