lint: enable intrange linter (#7331)

Enable intrange linter to enforce modern Go range syntax over
traditional for loops, by converting:

for i := 0; i < n; i++

to:

for i := range n

Adding type conversions where needed for compatibility
with existing uint64 parameters.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

test/proxy_test.go

@@ -71,7 +71,7 @@ func BenchmarkProxyLookup(b *testing.B) {
 	m.SetQuestion("example.org.", dns.TypeA)
 
 	b.ResetTimer()
-	for i := 0; i < b.N; i++ {
+	for range b.N {
 		if _, err := dns.Exchange(m, udp); err != nil {
 			b.Fatal("Expected to receive reply, but didn't")
 		}