utilize BaseSpOptExactSolver

[jGaboardi]

This PR removes the ortools import in BaseClass so that BaseSpOptExactSolver can then be inherited by LocateSolver instances.

xref #298 #49

[codecov]

Codecov Report

Merging #305 (a0e8465) into main (21fe3e0) will increase coverage by 0.2%.
The diff coverage is 75.0%.

@@           Coverage Diff           @@
##            main    #305     +/-   ##
=======================================
+ Coverage   73.7%   73.9%   +0.2%     
=======================================
  Files         23      23             
  Lines       2421    2417      -4     
  Branches     463     463             
=======================================
+ Hits        1785    1786      +1     
+ Misses       578     573      -5     
  Partials      58      58             

Impacted Files	Coverage Δ
spopt/BaseClass.py	73.3% <50.0%> (+20.7%)	⬆️
spopt/locate/base.py	95.1% <100.0%> (ø)