Bibtex fails on common strings that can be variables on latex

[ifenghm]

I had an issue where the download fails upon certain papers with month abbreviation. adding an option to parse common strings not as variables fixes it.

python -m PyPaperBot --query "delve" --min-year 2024 --dwn-dir ./delvepapers --scholar-pages 1
                                                                                                                                                  

⎿ Traceback (most recent call last):
File "/Users/feng/theoreticalcs/automataproject/.venv/lib/python3.12/site-packages/bibtexparser/bibdatabase.py", line 105, in expand_string
self.strings[name])

in Paper.py, these below changes will fix the problem.

        parser = bibtexparser.bparser.BibTexParser(common_strings=True)
         x = bibtexparser.loads(bibtex, parser=parser)

I want to push to the DEV branch as listed in the README.md but do not have push access; I can push to a fork if necessary, thank you.