New ci to build with github actions instead of azure.

[luciansmith]

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[luciansmith]

So! I realized that we don't actually need to get this working after all; we could just rename the old files, since they were made with ctypes, not Swig. But if we do revive the project eventually, we'll need to start from here.

Note that things are on their way to working. Currently, different things go wrong on different platforms:

macos13 and ubuntu: Probably actually works. Only problem is that we need to cut the whole 'run several times on different pythons' bit that I stole from roadrunner; we instead just need a single python, a la Antimony.
macos14: Build problem with yajl_malloc_func that doesn't show up on any other platform.
windows: config problem with libxml2, I think?
manylinux: vcpkg action stops when complains that it's a different owner that whoever checked out vcpkg. Might need to set up vcpkg manually on this platform.