Region-k-means seed

[jGaboardi]

Resolves #213.

After more digging I found that we were not providing the functionality of actually passing in a seed value to the base._seeds() function. Therefore, the resultant numpy.random.choice() function within could never be reproduced and was screwing tests up.

This PR also:

• fills in all docstrings in base.py (xref fill and and standardize docstrings #173, short-to-mid term plan for improving docs, structure, and formatting #280)
• cleans up several raised error logics
• adds several more test cases
• removes unused RegionMixin()

[codecov]

Codecov Report

Merging #294 (6d44416) into main (de63bf2) will increase coverage by 0.3%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #294     +/-   ##
=======================================
+ Coverage   72.9%   73.2%   +0.3%     
=======================================
  Files         23      23             
  Lines       2402    2402             
  Branches     460     459      -1     
=======================================
+ Hits        1750    1758      +8     
+ Misses       584     580      -4     
+ Partials      68      64      -4     

Impacted Files	Coverage Δ
spopt/region/maxp.py	94.7% <ø> (ø)
spopt/region/base.py	97.6% <100.0%> (+6.4%)	⬆️
spopt/region/region_k_means.py	98.7% <100.0%> (+<0.1%)	⬆️

[jGaboardi]

@sjsrey @knaaptime gently pining for review (when time permits).

[sjsrey]

The seed stuff looks good. Just one question related to RegionMixin that I left.

[jGaboardi]

converted #297 to a discussion (#298)

[sjsrey]

Thanks for spotting the lack of use of RegionMixin