An interface to ChronosQ

[lelemmen]

Describe the feature you'd like
In order to calculate integrals of GIAOs, it would be nice if we don't have to implement our own integrals, but rather use an existing open-source alternative to just get the integrals. ChronusQ seems to be the only (?) package that offers these open-source integrals. Many of the possibilities of this package are listed in the article.

Describe what the current code offers in relation to what it lacks
We already have the buffer/engine classes, so we should figure out how to interface these classes with ChronusQ. Could a GI-GTO then be represented as SPBasis<GIGTOShell>?

Additional context
Libcint can only calculate integrals over GIAOs up to first order, i.e. an 1+x form instead of the exp(x) form.

If this package would be insufficient, we can resort to an Obara-Saika or McMurchie-Davidson implementation of the integrals, with complex Boys functions.