The previous version computed a SHA-256 of the frame into a variable
named `entropy` and then discarded it, drawing instead from the OS
CSPRNG via secrets.randbits(). The camera contributed nothing.
Replace with a NIST SP 800-90A HMAC-DRBG seeded from the frame hash so
the camera genuinely contributes entropy. Add --interval for loop
rate control, --out for writing raw bytes to a FIFO, mutual exclusion
of --loop/--single, and bit-multiple validation.
Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>
Radek