UserAgent

UserAgent class for handling user interaction within the agent framework.

Acts as a bridge between various user input sources (streams, web UI, etc.) and the message system. Supports pluggable input methods through the UserInputBase interface, allowing customization of how user input is collected and converted into framework messages.

Design Philosophy:

• UserAgent does NOT manage memory - it only captures user input

• Input is obtained via pluggable UserInputBase implementations

• Supports both simple text input and structured input with validation

• Can participate in MsgHub for multi-agent conversations

Usage Examples:

`// Simple console input (default)
UserAgent user = UserAgent.builder()
.name("User")
.build();
Msg input = user.call().block();

// With custom input method
UserAgent user = UserAgent.builder()
.name("User")
.inputMethod(myCustomInput)
.build();

// With hooks
UserAgent user = UserAgent.builder()
.name("User")
.hooks(List.of(myHook))
.build();
`