setup.py: Declare extras for the supported backends

[mkoeppe]

In addition to "cypari" and "cypari2", this declares an extra "passagemath", which pulls in the distribution https://pypi.org/project/passagemath-pari/ (which vendors a version of cypari2).

[MarkCBell]

Hi @mkoeppe,

While we could merge something like this in, if I understand passagemath-pari correctly, it provides a wrapper for cypari2 on its own. If so, we should look to rebuild this repo to use passagemath-pari directly.

I've already been able to do this on the https://github.com/MarkCBell/realalg/tree/feature/passagemath-pari experimental branch. This appears to work on linux / mac but I haven't been able to get the Window CI to build correctly (cysignal doesnt build), does passagemath-pari support windows? Are you able to offer any insights / tweaks to https://github.com/MarkCBell/realalg/blob/feature/passagemath-pari/.github/workflows/CI.yml to get this to build?

Best,
Mark

[mkoeppe]

Hi Mark,
Thanks for looking into this! Yes, Windows support is one of my goals for passagemath, but I haven't started work on it yet, so I don't have immediate suggestions.
Does cypari not depend on cysignals?
Matthias