Add streaming session and ability to use streaming

[Krivoblotsky]

What

1. Chats and Completions have been updated with streaming functionality
2. ChatStreamingResult has been created
3. Tests have been updated

Why

#14

Affected Areas

Completions, Chats

[DJBen]

If you want to mix the complete and partial results, can you comment in what condition these properties are nil?

I have moderate preference in separating a complete Choice from a PartialChoice, provided that they have major differences, despite the official OpenAI API mix them together.

// Choice stays the same

public struct PartialChoice: Codable, Equatable {
  struct Delta: Codable, Equatable {
    public let content: String?
    public let role: Chat.Role?
  }
  public let index: Int
  public let delta: Delta
}

As a result, the result can contain enum of either Choice or PartialChoice
What do you think? Appreciated!

[Krivoblotsky]

I've decided to keep ChatResultto not break backward compatibility and created "ChatStreamingResult" along with a separate function for streaming. I found this solution more straightforward and clean. What do you think about this?

[DJBen]

Since we are using two separate functions for the chats(query:) and chatStream(query:) to represent streaming and non-streaming version of the chat api, we can potentially get rid of the stream: Bool? property inside ChatQuery, and modify the encoder to serialize stream: false and stream: true respectively when calling these two different functions. But it's probably a large model change.

[DJBen]

I added streaming in the demo app #59

[Krivoblotsky]

It looks like everything is working as expected 🤞
Going to check more tests on weekends and proceed.
https://user-images.githubusercontent.com/1411778/235212448-0aa844d5-7ffb-487e-a0bb-37eed5666f48.mov

[DJBen]

Hi @Krivoblotsky do you know when this can be merged?

[Krivoblotsky]

Hi, @DJBen
I have plans for this week for this to be updated and merged.

[Krivoblotsky]

Hey, @DJBen.
I'm ready to merge it, but wanted to ask you for a review first 🙏

[DJBen]

LG!