data: Support some arithmetic expressions on mismatching types.

The following cases are now supported:
 - <integer> or <decimal> <mul> <datetime>
 - <datetime> <mul> or <div> or <mod> <integer> or <decimal>

Think of <datetime> having a time unit like seconds. It's perfectly fine to
multiply with or divide seconds by a number. However, since we don't have any
type having the unit Hertz, we cannot support numbers divided by <datetime>.