feat: find pi cation interactions

[Jaakik]

Add π-cation interaction detection

Adds find_pi_cation_interactions() function to biotite.structure.rings module for detecting interactions between aromatic rings and positively charged atoms.

• Follows same optimization patterns as find_stacking_interactions (vectorized operations, squared distances)
• Requires charge annotation to identify cations
• test with (3wip.cif) structure that includes cation-π interactions between the positively charged quaternary ammonium group of acetylcholine and aromatic residues in the binding pocket from Tryptophan and Tyrosine.

[padix-key]

Hi, thanks for the feature! I left a few comments below. In addition, could you add this function to doc/apidoc.json so it is findable in the API reference?

[codspeed-hq]

CodSpeed Performance Report

Merging #810 will not alter performance

_{Comparing Jaakik:feat/pi-cation-interactions (427ee57) with main (f796577)}

Summary

✅ 59 untouched benchmarks

[padix-key]

Thanks for the changes! I just fixed a typo in the doctest and wait until the CI passes.