Fix flaky random ZIP creation in TestPolyglotModule

[thomas-chauchefoin-tob]

See #162 for context. I think the user got (un)lucky and the randomly generated ZIP file looked like a valid Pickle object with 2+ valid opcodes.

[dguido]

Thanks for tracking this down! The fix is on the right track, but there's an issue: random.seed(42) doesn't affect os.urandom().

In create_random_zip():

def create_random_zip(filename, size=1024):
    tmp_filename = "".join(random.choices(...))  # ✅ Affected by seed
    with open(tmp_filename, "wb") as f:
        f.write(os.urandom(size))  # ❌ NOT affected by seed

os.urandom() reads from the OS cryptographic random source (/dev/urandom), which is independent of Python's random module. So the ZIP content remains non-deterministic.

To fully fix the flakiness, replace os.urandom(size) with random.randbytes(size) (available since Python 3.9):

f.write(random.randbytes(size))  # ✅ Respects random.seed()

This will make the entire test deterministic.