C unit tests should be incorporated into the CI

[jdavies-st]

There are C unit tests here

https://github.com/spacetelescope/drizzle/blob/master/src/tests/utest_cdrizzle.c

which use a vendorized framework fctx

https://github.com/imb/fctx

that is no longer maintained, plus some pandokia stuff. @jhunkeler any knowledge on either of these dependencies?

We should figure out if (and how) these can be compiled and get them into the CI, if they cannot be compiled, then duplicate these tests in python unit tests.

[jdavies-st]

And it goes without saying that we want to get rid of the pandokia-related code in the above tests.