amended clt_threshold behavior

[mgiulini]

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Closes #386. @amjjbonvin Now the calculation of the cluster-based caprieval scores is correct even if the cluster is underpopulated.

[codecov-commenter]

Codecov Report

Merging #460 (105d4ee) into main (7d5d4e1) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #460      +/-   ##
==========================================
- Coverage   71.02%   71.01%   -0.02%     
==========================================
  Files          91       91              
  Lines        5743     5741       -2     
==========================================
- Hits         4079     4077       -2     
  Misses       1664     1664              

Impacted Files	Coverage Δ
src/haddock/modules/analysis/caprieval/capri.py	78.60% <100.00%> (-0.12%)	⬇️
tests/test_module_caprieval.py	96.10% <100.00%> (ø)

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