Signed 1<<31 overflow disables Fortuna pool 31 from reseed schedule

Summary

Pool selection loop(:203-204) uses 1<<i on signed int. At i=31: 1<<31 = INT_MIN (UB). reseed_cnt%(sign-extended huge) never 0 -> break at i=31 -> pool[31] never finalized. Fortuna last pool provides long-term backtracking resistance. 31 effective pools instead of 32. Fix: 1ULL<<i.