PoC: Fixed-point arithmetic score

SimpleBigDecimalScore is expensive. Let's create SimpleMilliScore that uses fixed-point arithmetic with three decimal points. Inputs and outputs are doubles, but internal operations happen using fixed-point arithmetics.

Once the results of this experiment are evaluated, we can make a decision to invest in expanding this into all other types of score, and also whether to introduce micro- and pico- variants.

See the Zulip thread for discussion and pointers:
https://kie.zulipchat.com/#narrow/stream/235756-optaplanner-dev/topic/BendableScore.20backed.20by.20normal.20score.3F