Fix exploration transformations

[seancolsen]

Steps to reproduce

1. Run off the explorations branch used for Enabling running of very simple explorations #3855

2. Run a very simple exploration like this

   

3. Try to add a transformation.

4. Observe the following error:

   

   [-31002] AssertionError:
   Traceback (most recent call last):
     File "/code/mathesar/rpc/exceptions/handlers.py", line 16, in safe_func
       return f(*args, **kwargs)
     File "/code/mathesar/rpc/explorations.py", line 189, in run
       exploration_result = run_exploration(exploration_def, conn, limit, offset)
     File "/code/mathesar/utils/explorations.py", line 89, in run_exploration
       records = db_query.get_records(
     File "/code/db/queries/base.py", line 117, in get_records
       table=self.transformed_relation,
     File "/code/db/queries/base.py", line 187, in transformed_relation
       transformed = apply_transformations(
     File "/code/db/transforms/operations/apply.py", line 8, in apply_transformations
       relation = _apply_transform(relation, transform)
     File "/code/db/transforms/operations/apply.py", line 13, in _apply_transform
       assert isinstance(transform, Transform)
   AssertionError
   
   During handling of the above exception, another exception occurred:
   
   Traceback (most recent call last):
     File "/usr/local/lib/python3.9/site-packages/modernrpc/handlers/jsonhandler.py", line 182, in process_single_request
       result_data = _method.execute(context, args, kwargs)
     File "/usr/local/lib/python3.9/site-packages/modernrpc/core.py", line 143, in execute
       return self.function(*args, **kwargs)
     File "/code/mathesar/rpc/exceptions/handlers.py", line 18, in safe_func
       _raise_generic_error(e)
     File "/code/mathesar/rpc/exceptions/handlers.py", line 25, in _raise_generic_error
       raise RPCException(err_code, e.__class__.__name__ + ": " + str(e))
   modernrpc.exceptions.RPCException: [-31002] AssertionError:
   

[seancolsen]

Fixed in #3873