Refactor of utility C code for less duplication

[cmccully]

There was a lot of code duplication in the C code for medianing and dilating images. I have removed as much as possible in hopes of making it easier to update how edges are handled in the future as discussed in #38 . Note this is expected to be merged after #74.

[codecov[bot]]

Codecov Report

Merging #76 (0f2f955) into main (783f217) will increase coverage by 2.00%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main      #76      +/-   ##
==========================================
+ Coverage   93.09%   95.09%   +2.00%     
==========================================
  Files           7        6       -1     
  Lines         782      836      +54     
  Branches       12        0      -12     
==========================================
+ Hits          728      795      +67     
+ Misses         54       41      -13     

Impacted Files	Coverage Δ
astroscrappy/utils/median_utils.pyx	100.00% <ø> (ø)
astroscrappy/astroscrappy.pyx	83.53% <100.00%> (+5.84%)	:arrow_up:
astroscrappy/utils/image_utils.pyx	100.00% <100.00%> (ø)
astroscrappy/utils/imutils.c	100.00% <100.00%> (ø)
astroscrappy/utils/medutils.c	100.00% <100.00%> (ø)
astroscrappy/__init__.py

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[saimn]

@cmccully - Could you rebase now that #74 and #81 are merged ? You will have a few conflicts to resolve I guess... Also Cython 3.0 has been released :)