Add new event types

[jlowin]

This pull request includes significant refactoring and improvements to the event handling system in the controlflow package. The changes aim to simplify the event model, improve consistency, and enhance the functionality of event handlers.

A primary, tangible benefit of this PR is enhanced PrintHandler output by using the new public event hooks, e.g.:

printhandler.mp4

The following settings/env vars are respected:

enable_default_print_handler # default True
default_print_handler_show_completion_tools # default True
default_print_handler_show_completion_tool_results # default False

Refactoring and Simplification:

• Removed ToolCallEvent and ToolResultEvent classes, replacing them with AgentToolCall and ToolResult respectively in src/controlflow/events/events.py. [1] [2] [3] [4] [5]
• Updated methods to yield related events using the new all_related_events method in AgentMessage and AgentMessageDelta classes. [1] [2] [3]

Enhancements to Event Handling:

• Added CallbackHandler and AsyncCallbackHandler classes to handle events by calling a callback function.
• Introduced QueueHandler and AsyncQueueHandler classes to queue events, with optional filtering capabilities.

Code Consistency:

• Standardized the __repr__ method in the Event class for better readability.
• Updated import statements and type annotations for consistency and clarity across multiple files. [1] [2] [3]

Additional Changes:

• Introduced new methods in AgentMessage and AgentMessageDelta to convert messages to tool calls and content events, enhancing the modularity of event handling. [1] [2]
• Updated the message_compiler to use the new event classes and methods.

These changes collectively improve the maintainability and functionality of the event handling system in the controlflow package.