BUG: RNG pruning condition and loop bound

[dcodrut]

This PR fixes #801:

• Fix the Toussaint RNG-2 condition: prune $(i,j)$ if ∃ $k$: $\max(d_{ik}, d_{jk}) < d_{ij}$
• include last node: n = len(coordinates) and skip k == i or k == j
• Updated the test (the resulted graph in shown below)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.4%. Comparing base (44ede54) to head (f134a92).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #802   +/-   ##
=====================================
  Coverage   85.4%   85.4%           
=====================================
  Files        150     150           
  Lines      15971   15951   -20     
=====================================
- Hits       13632   13618   -14     
+ Misses      2339    2333    -6     

Files with missing lines	Coverage Δ
libpysal/weights/gabriel.py	91.2% <100.0%> (+0.1%)	⬆️
libpysal/weights/tests/test_gabriel.py	100.0% <100.0%> (ø)

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[jGaboardi]

Great catch on the @dcodrut ! Thanks for the PR