Add support for streaming chunks

[drnic]

Either pass a block to the chat() method with one or two arguments:

@client = Groq::Client.new(model_id: "llama3-70b-8192")

@client.chat("Write a long poem about patience") do |content|
  print content
end
puts

Or pass a Proc or callable object to stream: keyword argument:

class MessageBits
  def initialize(emoji)
    print "#{emoji} "
    @bits = []
  end

  def call(content)
    if content.nil?
      puts
    else
      print(content)
      @bits << content
    end
  end

  def to_s
    @bits.join("")
  end

  def to_assistant_message
    Assistant(to_s)
  end
end

bits = MessageBits.new("🍕")
@client.chat("Write a long poem about pizza", stream: bits)

Credit to https://github.com/alexrudall/ruby-openai/blob/main/lib/openai/http.rb for borrowed code