von mises speedup

[cscherrer]

Note: vm_draw_test is failing, and I'm not sure why.

But two new tests are passing:

• 2-sample KS comparing the sampler vs slice sampling
• Chi-square test comparing binned sample counts to Simpson's 1/3 rule partitions

So for now the old test is commented out

[schmidmt]

Looks good. Can't speak to the correctness of the draw algo but if the 2sample test works 🤷. Just one change.

[codecov]

Codecov Report

Attention: Patch coverage is 93.90244% with 5 lines in your changes missing coverage. Please review.

Project coverage is 80.81%. Comparing base (3d519bc) to head (94a7b2e).
Report is 1 commits behind head on release/v0.19.0.

Files with missing lines	Patch %	Lines
src/dist/vonmises.rs	93.90%	5 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                 @@
##           release/v0.19.0      #30      +/-   ##
===================================================
- Coverage            80.86%   80.81%   -0.06%     
===================================================
  Files                   98       98              
  Lines                19595    19656      +61     
  Branches             19595    19656      +61     
===================================================
+ Hits                 15846    15885      +39     
- Misses                3634     3656      +22     
  Partials               115      115              

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