Improve _updateStatus scale-down

[MrToph]

Changes to _updateStatus:

• removed the final numerator computation as this variable is never read after it has been written
• we only need to reduce the new final filled fraction, the numerator fill value becomes irrelevant in this function. This means we can just compute the gcd of filledNumerator and denominator.

[0age]

oh interesting, this breaks some of the direct tests; it's possible that we need to review those and update the values as scaleDown is more permissive with this change

[MrToph]

I see, some of these values are currently hardcoded in tests. I can just update them. 6/10 is the same as 3/5.