HV3D+ preprocessing: Fix bug related to repeated coordinates

[apguerreiro]

This pull request fixes a bug in the preprocessing procedure of HV3D+ related to repeated coordinates. A testcase for this bug is:

0.5 0.5 0.1
0.4 0.5 0.2
0.3 0.5 0.3
0.2 0.5 0.4
0.1 0.1 0.5

Although the bug should not lead to incorrect results when using HV3D+, the data structure is not setup as intended. A side effect is that the preprocessing may take longer because the AVL tree may (unnecessarily) keep many points that are weakly dominated in the (x,y)-plane. To check this, we can use a testcase with $n$ points generated like this:

$p^i = (\frac{i-1}{n}, 0.5, 1-\frac{i-1}{n})$ for all $i=1,...,n$.

For large $n$, it is possible to see that the previous version of the code would take longer.

[codecov]

Codecov Report

❌ Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.49%. Comparing base (2c66c8a) to head (589b9ae).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #41      +/-   ##
==========================================
+ Coverage   73.39%   73.49%   +0.10%     
==========================================
  Files          58       58              
  Lines        5041     5049       +8     
  Branches      964      970       +6     
==========================================
+ Hits         3700     3711      +11     
+ Misses        964      961       -3     
  Partials      377      377              

Flag	Coverage Δ
R	78.68% <ø> (ø)
python	72.60% <44.44%> (+0.12%)	⬆️

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Components	Coverage Δ
tests	100.00% <ø> (ø)
src	86.99% <ø> (ø)

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[MLopez-Ibanez]

Thank you!

Rather than removing the assertion, I have relaxed it to accept area == 0 (but not area < 0).

I have also added the testcase to the testsuite (with all permutations of the columns): multi-objective/testsuite@5b3fa6d