mark by_col() methods as deprecated

[jGaboardi]

mark by_col() methods as deprecated

see #305

the tests for the Moran*.by_col() methods have been deprecated and marked for removal "in the next release" (though that seems to have been ≈4 years ago), but is no actual indication the methods themselves are marked as such. For example, Moran_Tester.test_by_col() is marked deprecated, but there is nothing mentioning that in Moran.by_col()

---

• This first commit deprecates by_col() methods in moran.py
• Do we also need to start deprecating the by_col() methods in other modules & classes? -- xref Moran*.by_col() methods deprecated? #305 (comment)

[codecov]

Codecov Report

❌ Patch coverage is 16.66667% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.1%. Comparing base (320a005) to head (9f0fa94).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
esda/moran.py	16.7%	10 Missing ⚠️

❌ Your patch status has failed because the patch coverage (16.7%) is below the target coverage (60.0%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##            main    #456     +/-   ##
=======================================
- Coverage   82.3%   82.1%   -0.2%     
=======================================
  Files         27      27             
  Lines       3961    3973     +12     
=======================================
+ Hits        3258    3260      +2     
- Misses       703     713     +10     

Files with missing lines	Coverage Δ
esda/moran.py	83.6% <16.7%> (-1.3%)	⬇️

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[jGaboardi]

@sjsrey -- since this is simply marking the by_col() methods in Moran with a future removal warning, shall we go ahead merge. Nothing is being removed here.