Add generic aromatic bond

[padix-key]

The kekulized form of aromatic bonds (i.e. their representations as single, double or triple bonds) is a visualization artifact: Chemically aromatic bonds have no bond order, but the pi-elections are delocalized in the entire pi-system.

For this reason I think it makes sense to lift the restriction to assign a bond to either of AROMATIC_SINGLE, AROMATIC_DOUBLE or AROMATIC_TRIPLE, but to allow a generic AROMATIC as well. Although, this might lead to some limitations in visualization, there are some advantages

• Models predicting aromatic bonds do not necessarily need to know the kekulized form.
• Some software does not internally represent aromatic bonds in kekulized form (e.g. RDKit).
• SDF and PDBx support generic aromatic bonds as well.

[codspeed-hq]

CodSpeed Performance Report

Merging #738 will not alter performance

_{Comparing padix-key:aromatic-bond (2b0f6d9) with main (8138e0e)}

Summary

✅ 59 untouched benchmarks