Add sufficient statistics and MLE for `Chi` and `Chisq`

[devmotion]

[codecov-commenter]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 86.32%. Comparing base (a1b8bb3) to head (a9b1790).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1997      +/-   ##
==========================================
+ Coverage   86.28%   86.32%   +0.03%     
==========================================
  Files         146      146              
  Lines        8787     8803      +16     
==========================================
+ Hits         7582     7599      +17     
+ Misses       1205     1204       -1     

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.