possibly a fix for inkscape 1.2.x#3

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liam-o-marsh wants to merge 3 commits intobriling:masterfrom

liam-o-marsh:backports

Commits on Sep 2, 2023

more fixes for more recent inkscape versions, plus comments and asserts
liam-o-marsh
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refactoring: splitting classes, changing inner interfaces for bond solving
liam-o-marsh
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Commits on Sep 3, 2023

refactor: do not use print() in 'library code'
liam-o-marsh
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