feat(zingela): M2 address engine - cyclic-group permutation + exclude floor
Stateless O(1) zmap-style multiplicative cyclic group: runtime smallest-
prime-above-N (deterministic Miller-Rabin), fresh CSPRNG primitive root
validated against the factors of p-1, two-ops-per-target iteration with
near-zero re-roll.
numtheory.zig: modExp/mulMod (u128 intermediate), isPrime, smallestPrimeAbove,
distinctPrimeFactors, primitive-root finder, all with known-answer tests.
targets.zig: CIDR parse, RFC 6890 reserved exclude floor by range subtraction
(reserved space never enters the index space), cumulative-prefix IpPicker,
mixed-radix IP:port decode, contiguous pizza-slice sharding with a fail-closed
shard-count guard. Full bijection property tests (single shard + 4-shard union,
no gaps/overlap/reserved), green Debug + ReleaseSafe, leak-free.
c9d0cf5e36