* Move AgentSession.Serialize to AIAgent
* Address PR comments.
* Improve code and fix unit test
* Update test agents to return a default json element instead of throwing where the the result of the serialization is never used.
* Update further tests to actually serialize the session
* refactor: Rename AggregateTurnMessagesExecutor
* feat: Rework Agent Hosting for Configurability and HIL support
* Adds support for selecting whether updates and/or full responses are
emitted to events
* Adds support for HIL/FunctionCalls (including interception)
* Implements internal support for ExternalRequests from any executor
(not just RequestPort)
* test: Add tests for new AIAgentHostExecutor functionality
* feat: Unify non-Handoff Agent Hosting
* doc: More explicit documentation for `overwrite` in RouteBuilder