* refactor: replace InstanceOf[T] with plain type annotations
InstanceOf[] is a Pydantic validation wrapper that adds runtime
isinstance checks. Plain type annotations are sufficient here since
the models already use arbitrary_types_allowed or the types are
BaseModel subclasses.
* refactor: convert BaseKnowledgeStorage to BaseModel
* fix: update tests for BaseKnowledgeStorage BaseModel conversion
* fix: correct embedder config structure in test