that would mean one additional dependency for us (from yet another maintainer), which is not even pure python
we only use bitstring for bolt11-parsing
hence this PR rewrites the bolt11-parsing and removes bitstring as dependency
note: I benchmarked lndecode using this, and the new code performs better,
taking around 80% time needed for old code (when using bitstring 3.1.9, pure python).
Though the variance is quite large in both cases.
bitstringstarted depending onbitarrayin version 4.1bitstringas dependency