Add zig build fuzz, dispatching to named seeded targets in fuzz_tests.zig via a tuple->FieldEnum table, plus bench/smoke stubs that fail until those milestones land. delta_fuzz.zig parameterizes the existing apply/create/ decodeInt property checks by seed and round count for an out-of-band runner. delta.zig gains an allocation-failure test for apply() mirroring create()'s, and a targetSize() garbage-never-crashes block. check-in: c4c4ad80d1 user: dmestas tags: trunk