Streaming with tools

[Vein05]

#48 Added this functionality. To use it you need to call the Delta with Tool calls, and everything works normally as the TooCalls.

// StreamDelta represents a delta in the chat completion stream.
type StreamDelta struct {
	Role             string     `json:"role,omitempty"`              // Role of the message.
	Content          string     `json:"content"`                     // Content of the message.
	ReasoningContent string     `json:"reasoning_content,omitempty"` // Reasoning content of the message.
	ToolCalls        []ToolCall `json:"tool_calls,omitempty"`        // Optional tool calls related to the message.
}