Simple input/output type validation on the LogicalPlan layer. Note: this doesn't work on the execution layer (SycamoreExecutor) which can have it's own set of validations that are more dynamic and implementation specific.

Next steps:

1. add schema validations (e.g. nodes that read fields, can assert that the field exists in the schema or has been added to the data in the query)
2. llm planner correction, get the llm to fix it's plan