Clarify notion of "const"

[mforets]

From The SpaceEx modelling language,

The parameters rup, rdown, ton, tof f are formal parameters that we need to declare
for the component. They are real-valued and scalar, and as parameters of a hybrid
automaton they do by definition not change their values during an execution of the
automaton. In the SX format, this is called const dynamics.

However, some models have dynamics = "const" for input variables (typically u) which do not explicitly have u' == 0 as a dynamical equation.

[schillic]

some models have dynamics = "const" for input variables (typically u) which do not explicitly have u' == 0 as a dynamical equation.

I think this is a misuse and should result in an error.