consider SciPy BDF solver as alternative to VODE

[zingale]

The SciPy BDF solver looks quite clean and is implemented completely in python: https://github.com/scipy/scipy/blob/main/scipy/integrate/_ivp/bdf.py

in the pynucastro comparisons, this seemed to perform well compared to VODE, and might make for a good alternative

[psharda]

+1 for this idea. BDF works well for the primordial_chem stuff too.

[zingale]

note that that is what VODE is -- it is BDF. It is just a different implementation.

[zingale]

closing this in favor of the new RKC integrator we are experimenting with now