Add cl_scalar*cl_vector operators.
Helper trait to add scaling to expressions:
`expr * factor`, `factor * expr` and `expr / factor` return a new expression where the factor has been applied to the `scale` field.
Support appending and adding FFT
Revert "Move UserFunction body to value level."

This reverts commit 4fdc2e3c11f8e4e66466e54606d4b081fd854918.
values, not types