pkg: synthetic
note: test benchstat printing of units

BenchmarkTwoHourMarathon 1 7200000000000 ns/op 14400000000000 user-ns/op 5 ns/GC 12 quick-bytes
BenchmarkTwoHourMarathon 1 7200000000000 ns/op 14500000000000 user-ns/op 5 ns/GC 16 quick-bytes
BenchmarkTwoHourMarathon 1 7200000000000 ns/op 14600000000000 user-ns/op 5 ns/GC 12 quick-bytes
BenchmarkTwoHourMarathon 1 7200000000000 ns/op 14200000000000 user-ns/op 5 ns/GC 16 quick-bytes
BenchmarkTwoHourMarathon 1 7200000000000 ns/op 14300000000000 user-ns/op 5 ns/GC 12 quick-bytes