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.