It's always been commonly said to 'ignore' that TPS was '19.X', that
it was fine.
I suspect that the inaccuracy of floating point math resulted in us
losing precision over time, making it difficult to actually get back to 20,
as you know the fun 0.1 + 0.1 ... 9 more times != 1 problem.
BigDecimal supports working with doubles with higher precision.
This change makes it so our RollingAverage class maintains all of the data
using BigDecimal and using BigDecimal arithematic operations.
This ensures we have extremely high precision, enabling us to
actually be able print '20 TPS' when TPS is perfect.
computeIfAbsent would leak as the entry
was never registered into the ttl map
This fixes that ,as well as redesigns cleaning to
not run on every manipulation, and instead to run clean
once per tick per expiring map.
Aikar