#797 CIF type checker: check for single-value types of declarations.

• Best to review per commit.
• Design decisions:
  • Check the types of algebraic parameters, algebraic variables, discrete variables, event parameters, events, function parameters, function local variables, function return types, and input variables.
  • Do not check for constants, as introducing named constants for a single value seems like a valid use case.
  • Do not check for type declarations, but only for the use of types. If users want to name the type of a single-valued type for a constant, that should be possible.

Closes #797 (closed)