cephes: format code and add tests

[inkydragon]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 27.38249% with 1684 lines in your changes missing coverage. Please review.

Project coverage is 27.69%. Comparing base (6c8762d) to head (f8e3dde).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
cephes/cprob/incbet.c	2.53%	192 Missing ⚠️
cephes/cprob/incbi.c	2.46%	158 Missing ⚠️
cephes/polyn/polyn.c	0.00%	152 Missing ⚠️
cephes/polyn/polrt.c	0.00%	113 Missing ⚠️
cephes/misc/polylog.c	5.30%	107 Missing ⚠️
cephes/polyn/euclid.c	0.00%	96 Missing ⚠️
cephes/cprob/kolmogorov.c	0.00%	65 Missing ⚠️
cephes/cprob/stdtr.c	0.00%	64 Missing ⚠️
cephes/misc/beta.c	11.11%	56 Missing ⚠️
cephes/cprob/bdtr.c	0.00%	52 Missing ⚠️
... and 32 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #8      +/-   ##
==========================================
+ Coverage   26.32%   27.69%   +1.36%     
==========================================
  Files         144      144              
  Lines        5196     5196              
  Branches      485      745     +260     
==========================================
+ Hits         1368     1439      +71     
+ Misses       3828     3757      -71     

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