eval: a note for later about why we can't implement Call for device types
eval: a note for later about why we can't implement Call for device types

A little refactoring is required so that call implementations can get
access to the eval context, which is tricky because calls are mediated
by code in cbty and it doesn't have any awareness of eval.Context.

cirbo-lang/cirbo,cirbo-lang/cirbo,cirbo-lang/cirbo