Cache the size and the do bit whenever someone asked for it. We can
probably add more:
PASS
BenchmarkStateDo-4 100000000 11.9 ns/op
BenchmarkStateSize-4 5000000 265 ns/op
ok github.com/miekg/coredns/middleware 2.828s
PASS
BenchmarkStateDo-4 1000000000 2.86 ns/op
BenchmarkStateSize-4 500000000 3.10 ns/op
ok github.com/miekg/coredns/middleware 5.032s
This PR also includes some testing cleanups as well.