* refactor: Unify ExecutorIsh and ExecutorRegistration => ExecutorBinding
* Switch to more modern Record type-tree for Sum Types
* Unify APIs for getting ExecutorBinding
* Fix an issue where workflows consisting entirely of cross-run shareable executors which are not instance-resettable do not properly clear state when running non-concurrently.
* feat: Simplify function-to-executor pattern
* refactor: Normalize API naming
* 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