examples no longer require any explicit closing to avoid
leaking.

That the tee-based examples still do is (I think) still a
mystery.  Part of the mystery is that gc.garbage remains
empty:  if it were the case that some generator in a trash
cycle said it needed finalization, suppressing collection
of that cycle, that generator _would_ show up in gc.garbage.

So this is acting more like, e.g., some tp_traverse slot
isn't visiting all the pointers it should (in which case
the skipped pointer(s) would act like an external root,
silently suppressing collection of everything reachable
from it(them)).