Add mardia watson wheeler

[GanshengT]

Hello Raphael and Pingouin community,

I have implemented the Mardia-Watson-Wheeler test in Pingouin (regarding feature request in issue #214). Hope this feature is useful.

Gansheng Tan

[codecov]

Codecov Report

Attention: Patch coverage is 80.55556% with 7 lines in your changes missing coverage. Please review.

Project coverage is 98.35%. Comparing base (c939d2d) to head (fc38b4e).

Files with missing lines	Patch %	Lines
src/pingouin/circular.py	80.55%	4 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #467      +/-   ##
==========================================
- Coverage   98.54%   98.35%   -0.20%     
==========================================
  Files          19       19              
  Lines        3360     3395      +35     
  Branches      492      496       +4     
==========================================
+ Hits         3311     3339      +28     
- Misses         26       30       +4     
- Partials       23       26       +3     

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