This _should_ only happen when we’re doing a partial PGO build, since
then the script is run in the parent terminal. In this case, the user
is expected to use --rows/--cols anyway.
Using Python's own PRNG should make the code cleaner and allow for
reproducible stimulus files if that is desired via setting --seed (at
least for the same versions of the script, changing the kind and/or
order of the random calls will of course impact the output in the
future).
I did the following substitutions:
* rand.read(1)[0] % n and struct.unpack('@H', rand.read(2))[0] % n →
random.randrange(n)
* rand.read(1)[0] → random.randrange(256)
* rand.read(n) → [random.randrange(256) for _ in range(n)]
(better alternative would have been random.randbytes(n), but is only
available for Python >= 3.9, switching to this in the future will
impact output)
* list[rand.read(1) % len(list)] → random.choice(list)
