Create ixa-stats

[k88hudson-cfa]

Let's prototype something we can use that exports rand-distr and utility functions from statrs

• separate crate
• in the mono repo, for now

[RobertJacobsonCDC]

See, for example, the manual implementations of cumulative density and probability mass functions in this PR: https://github.com/CDCgov/ixa-epi-isolation/pull/284/files.