New attributes & functionality for locate models

[jGaboardi]

This PR:

• resolves pre-defined facilities for all location models? #267
• resolves maybe set solver as attribute in LSCPB? #282
• resolves get_backup_percentage method for LSCP-B #283
• resolves remove BaseOutputMixin from PDispersion #285
• resolves calculate get_mean_distance() within PMedian.solve(results=True) #286
• resolves calculate get_percentage() within MCLP.solve(results=True) #287
• reruns notebooks to demonstrate new functionality & attributes
• starts a cleans up and standardization of docstrings (this will continue in future PRs)
• starts a cleanup and debugging of doctests (this will continue in future PRs)
  • all doctests in locate now pass, but ones region need much work (xref fill and and standardize docstrings #173, short-to-mid term plan for improving docs, structure, and formatting #280)

[jGaboardi]

xref #295 needs attention in the short term.

[codecov]

Codecov Report

Merging #296 (8c072af) into main (799cd86) will increase coverage by 0.5%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #296     +/-   ##
=======================================
+ Coverage   73.2%   73.7%   +0.5%     
=======================================
  Files         23      23             
  Lines       2402    2421     +19     
  Branches     459     463      +4     
=======================================
+ Hits        1758    1785     +27     
+ Misses       580     578      -2     
+ Partials      64      58      -6     

Impacted Files	Coverage Δ
spopt/locate/util.py	100.0% <ø> (ø)
spopt/locate/base.py	95.1% <100.0%> (+0.1%)	⬆️
spopt/locate/coverage.py	100.0% <100.0%> (+1.0%)	⬆️
spopt/locate/p_center.py	100.0% <100.0%> (+1.5%)	⬆️
spopt/locate/p_dispersion.py	100.0% <100.0%> (+9.3%)	⬆️
spopt/locate/p_median.py	100.0% <100.0%> (+1.5%)	⬆️

[gegen07]

hey @jGaboardi! Wow, nice improvements! I made minor comments.