Fix integration pipeline

This MR fixes several issues with the integration pipeline.

1. !349 (closed).

2. Fixes an oversight introduced in !344 (merged). The issue was with expressions like:

   a: scalar float = CastFunc(b: vector float, float)

   The mentioned MR used get_type_of_expression to determine whether an expression will be vectorized. That works in most cases due to type collation but fails for CastFuncs, which are always vectorized. This MR replaces get_type_of_expression by a small helper function that checks whether an expression is entirely scalar or requires additional vector casts.

pystencils/cpu/kernelcreation.py

@@ -130,7 +130,9 @@ def create_indexed_kernel(assignments: Union[AssignmentCollection, NodeCollectio
     assert len(spatial_coordinates) == 1, f"Non-index fields do not have the same number of spatial coordinates " \
                                           f"Non index fields are {non_index_fields}, spatial coordinates are " \
                                           f"{spatial_coordinates} and len(spatial coordiantes) is " \
-                                          f"{len(spatial_coordinates)}"
+                                          f"{len(spatial_coordinates)}, " \
+                                          f"index_fields in config: {config.index_fields}, " \
+                                          f"extracted index fields: {index_fields} "
     spatial_coordinates = list(spatial_coordinates)[0]
 
     def get_coordinate_symbol_assignment(name):