remove numba cache from fisher jenks

[martinfleis]

Numba is writing cache to tmp file in __pycache__ in the environment's site packages. If you install your conda env with admin rights and then try to run mapclassify with user rights, this will fail, as @jorisvandenbossche noticed while teaching.

The cache is there to cache JIT-ted version of the function so it does not have to be compiled in a new Python runtime again. There's a lot of gotcha's in the docs for caching, plus the one above. I suppose that the benefit of caching is in the end smaller than the issues it may cause, so I am suggesting removing cache=True.

[codecov]

Codecov Report

Merging #197 (6aeb3ae) into main (4417d31) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #197   +/-   ##
=====================================
  Coverage   89.4%   89.4%           
=====================================
  Files          8       8           
  Lines       1088    1088           
=====================================
  Hits         973     973           
  Misses       115     115           

Files	Coverage Δ
mapclassify/classifiers.py	88.4% <100.0%> (ø)

[jGaboardi]

@martinfleis Good to merge?

[martinfleis]

good from my side. so unless someone prefers to keep caching here, yes.

[jGaboardi]

We can revert if someone has a strong opinion later.