tests, native: fixup for cpuid

- adopt test name to new scheme
- check memory bounds some more
I think it is better if `CPUID_ID_LEN` is always at least `(4)` rather than `sizeof(_native_id)`, and may be even bigger. Real serial numbers for CPUs are in the range of 96 or 128 bits and since native is more of a test platform we should allow the user to experiment with IDs of this length on native.