A float ghost crashes the verifier: "Ghost not implemented for type float" #443

Declaring a float ghost crashes the verifier when the ghost needs its default value. The result should be either support for the type or a proper error at the @Ghost annotation.

Reproducer:

import liquidjava.specification.Ghost;
import liquidjava.specification.StateRefinement;

@Ghost("float level")
class Tank {
    @StateRefinement(to = "true")
    public void fill() {}
}

public class Main {
    public static void main(String[] args) { Tank t = new Tank(); t.fill(); }
}

Found on main @ f7f366c (also on 1a506fe):

Exception in thread "main" java.lang.RuntimeException:
Error while checking CtConstructorImpl
  on null
  at (no source position: CtConstructorImpl)
  with Ghost not implemented for type float
	at liquidjava.processor.refinement_checker.TypeChecker.scan(TypeChecker.java:99)
	...

int and boolean ghosts get defaults (0, false); double was not tried. Expected: a default for float too (or a user-facing error naming the supported ghost types).

Found while cataloguing spec forms for co-specification (probe V19 there). Low priority.