docs & typehints - artifacts.py.{ccss_special_case(), filter_connections()}

[jGaboardi]

This PR:

• adds docs & typehints for artifacts.py.{ccss_special_case(), filter_connections()}
• does a very small refactor inside filter_connections()
• several typos of "linestring" --> "linestrings"
• xref testing, refactor, & docstrings #20

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.8%. Comparing base (43e1da6) to head (ba1b1da).
Report is 4 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #127   +/-   ##
=====================================
  Coverage   98.8%   98.8%           
=====================================
  Files          6       6           
  Lines        962     966    +4     
=====================================
+ Hits         950     954    +4     
  Misses        12      12           

Files with missing lines	Coverage Δ
sgeop/artifacts.py	97.9% <100.0%> (+<0.1%)	⬆️

... and 1 file with indirect coverage changes