[BUG] Incomplete bounding of expressions with products or powers

[arnaud-m]

Describe the bug

The computation of bounds of the auxiliary variable is not accurate for mul or pow expressions.
It raises an exception because it does not take into account the right member of the relation.

However, the constraint times does not meet the same issue.

To Reproduce

Define the model below.

Model m = new Model();
IntVar[] x = m.intVarArray("x", 3, 0, IntVar.MAX_INT_BOUND);        
model.times(x[0], x[1], x[2]).post(); // Valid and posted
x[0].mul(x[1]).eq(x[2]).post(); // Valid, but raise an exception

The issue is also encountered with pow expression.

x[0].pow(x[1]).eq(x[2]).post(); // Valid, but raise an exception

Expected behavior
No exception.

[cprudhom]

I can sharp the bounds computed in VariableUtils to [IntVar.MIN_INT_BOUND, IntVar.MAX_INT_BOUND].
That will not fail anymore in the cases you depicted (well, the one with pow should be reduced, because there is no power constraint, it is turned into a table constraint).

BUT, the following example (from cryptator) will be problematic:

Model model = new Model("copper*neon=iron*silver");
IntVar copper = model.intVar("copper", 100000, 999999);
IntVar neon = model.intVar("neon", 1000, 9999);
IntVar iron = model.intVar("iron", 1000, 9999);
IntVar silver = model.intVar("silver", 100000, 999999);
copper.mul(neon).eq(iron.mul(silver)).post();

Indeed, the bounds of the intermediate variable for copper.mul(neon) will be [100000000L, 9998990001L] and an exception will be raised because the intermediate variable cannot be instantiated to an int value.