kumulant

TODO:

Implement Ridge/Lasso

histogram algos

• ddsketch
• frugal streaming
• T digest
• HDR
• reservoir
• linear

cardinality

• hyperloglog
• linear counting (bitset)

pgbm stuff

• vector of variance
• gradient sum (sumGrad+sumHess). this is probably just a paired sum
• crps (continuous ranked probability score)