* Rename WorkflowOutputEvent.SourceId to ExecutorId for Python consistency
- Rename SourceId property to ExecutorId in WorkflowOutputEvent
- Add [Obsolete] SourceId property for backward compatibility
- Update all test usages to use ExecutorId
Resolves part of #2938
* Unify AgentResponse events with WorkflowOutputEvent (#2938)
- Change AgentResponseEvent and AgentResponseUpdateEvent to inherit from
WorkflowOutputEvent instead of ExecutorEvent
- Update AIAgentHostExecutor and HandoffAgentExecutor to use YieldOutputAsync()
instead of AddEventAsync() for agent outputs
- Add special-casing in InProcessRunnerContext.YieldOutputAsync() to create
specific event types for AgentResponse and AgentResponseUpdate, bypassing
OutputFilter for backwards compatibility
- Update TestRunContext and TestWorkflowContext with same special-casing
- Add regression tests in AgentEventsTests
* refactor: Seal AgentResponse events
* refactor: remove unused internals
* feat: Execution Mode for sharing a workflow among concurrent runs
* feat: Update WorkflowHostAgent to support concurrent execution
* Also update AsAgent APIs to support injecting a CheckpointManager and an IWorkflowExecutionEnvironment
* fix: Make Read logic consistent in DeclarativeWorkflowContext