Csprng

How weak cryptographic randomness happens in C CSPRNG fallback paths and how to fix it

A critical vulnerability in `lib/sp_crypto.c` allowed the CSPRNG function to fall back to predictable randomness based on `time(NULL)` XORed with a counter when `/dev/urandom` was unavailable. An attacker who knew the approximate generation time could brute-force the output. The fix removes the unsafe fallback entirely, failing fast instead of silently degrading to weak randomness.