[pyos][design] Use `bibtexparser` to render bibtex

[sneakers-the-rat]

Part of: pyOpenSci/software-submission#267 (comment)

The package already depends on bibtexparser to parse bibtex, yet it has its own string-manipulation based bibtex formatter too. Bibtex is a weird format and this implementation is almost certainly wrong, and unnecessarily so. It would reduce complexity and improve accuracy to use a matured package to handle bibtex rather than rolling your own

https://bibtexparser.readthedocs.io/en/main/quickstart.html#step-3-exporting-with-defaults