> Py_DECREF calls in the C code

I think this part specifically is already covered through refleak
checks: https://github.com/python/cpython/blob/master/Lib/test/libregrtest/refleak.py

Since it can involve the repetition of tests many times, these aren't
run on the CI though, they do get run on the refleak buildbots so
issues get caught eventually:
https://buildbot.python.org/all/#/builders?tags=%2Brefleak

But again this is for PyObjects only. Were you able to find any memory
leaks with your proof-of-concept? I don't think there's a lot of
chances of someone missing a PyMem_Free call and there's not a lot of
other manual memory management but I could be wrong. Anything found
there could help motivate adding this a bit more.