greatroar 1e2379df1b
lib/protocol: faster Luhn algorithm and better testing (#6475)
The previous implementation was very generic; its tests didn't cover the
actual alphabet for device IDs.

Benchmark results on amd64:

name         old time/op    new time/op     delta
Luhnify-8      1.00µs ± 1%     0.28µs ± 4%   -72.38%  (p=0.000 n=9+10)
Unluhnify-8     992ns ± 2%      274ns ± 1%   -72.39%  (p=0.000 n=10+9)
2020-03-29 22:28:04 +02:00
..
2020-03-03 22:40:00 +01:00