feat(ChatEndpoint): implement TODO Streaming endpoints

[XRSPACEHugo]

public async Task StreamCompletionAsync(Action<ChatResponse> resultHandler, ChatRequest chatRequest, CancellationToken cancellationToken = default)
        {
            chatRequest.Stream = true;
            var jsonContent = JsonConvert.SerializeObject(chatRequest, Api.JsonSerializationOptions);
            using var request = new HttpRequestMessage(HttpMethod.Post, $"{GetEndpoint()}/completions")
            {
                Content = jsonContent.ToJsonStringContent()
            };
            var response = await Api.Client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
            await response.CheckResponseAsync(cancellationToken);
            await using var stream = await response.Content.ReadAsStreamAsync();
            using var reader = new StreamReader(stream);

            while (await reader.ReadLineAsync() is { } line)
            {
                if (line.StartsWith("data: "))
                {
                    line = line["data: ".Length..];
                }

                if (line == "[DONE]")
                {
                    return;
                }

                if (!string.IsNullOrWhiteSpace(line))
                {
                    resultHandler(DeserializeResult(response, line.Trim()));
                }
            }
        }

        private ChatResponse DeserializeResult(HttpResponseMessage response, string json)
        {
            var result = JsonConvert.DeserializeObject<ChatResponse>(json, Api.JsonSerializationOptions);

            if (result?.FirstChoice == null)
            {
                throw new HttpRequestException($"{nameof(DeserializeResult)} no completions! HTTP status code: {response.StatusCode}. Response body: {json}");
            }

            result.SetResponseData(response.Headers);

            return result;
        }

[XRSPACEHugo]

And make ChatResponse inherit BaseResponse :)

[XRSPACEHugo]

BTW, I found
https://api.openai.com/v1/chat/completions will give us wrong data structure,
According to the document it will send back "message" in "choice"

but we will get "delta" instead of "message" and make it deserialize wrong