refactor: share value scaling between RatchetAmount and RatchetProbability

[nikodemus]

• Math is exactly the same, call it compute(Current|Final)ValueForRatchets().

[github-actions[bot]]

Test Results

46 tests  ±0   46 :white_check_mark: ±0   1s :stopwatch: -1s  8 suites ±0    0 :zzz: ±0   8 files   ±0    0 :x: ±0 

Results for commit 38ddbf7c. ± Comparison against base commit 35131d27.

This pull request removes 1 and adds 1 tests. Note that renamed tests count towards both.

``` ValueScalingTest ‑ arpMidiCvRatchetAmountValueScaling ``` ``` ValueScalingTest ‑ arpMidiCvRatchetValueScaling ```