Validation check for auto-constructors

[dbera]

Auto-constructors have now been implemented for each update function of an output place of a transition.
However for initialization, i.e., value of initial tokens, no auto-constructors are possible. We rely on the user to have defined all the fields that will be referenced in the updates of the transitions that directly consume these initial tokens.
Note that subsequence production and consumptions are type safe due to auto-constructors in update functions.

[dbera]

@raulmonti We need to rethink auto-constructors.

Consider an action (pspec syntax)
action f
with-inputs: a
produces-outputs: a
updates:
a = a

Current Python Translation:
f(a):
a = a
return a

---

If we want to do auto-constructors for all produces outputs, the python implementation under-the-hood will do:

f(a):
a = 0 # auto-constructor value
a = a
return a

This is wrong, since the input value of a is overwritten by 0!!