Fix a bug with the current implementation of the NumericPercentile Constraint

[kklein]

Previously, the percentile computation was not according to the definition we provided ourselves.

Our definition said that

The percentile is defined as the smallest value present in column for which percentage % of the values in column are less or equal.

Let's now assume we have the following data

value	rank	rank/n
1	1	1/19 ~ .05
2	2	2/19 ~ .11
3	3	3/19 ~ .16
4	4	4/19 ~ .21
...	...	...
19	19	19/19 = 1

If we set the percentile of interest to be 20%, we see that the value 4 is the smallest value present in the data, for which at least 20% of the data is lesser or equal to that value.

Previously, our retrieval would've yielded 3. This behavior is explicitly reflected in our own tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.36%. Comparing base (1f9280c) to head (eb6eb14).
Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #241      +/-   ##
==========================================
+ Coverage   93.35%   93.36%   +0.01%     
==========================================
  Files          18       18              
  Lines        1985     1988       +3     
==========================================
+ Hits         1853     1856       +3     
  Misses        132      132              

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[ivergara]

If you plan on releasing right away you can fix the changelog file before merging.