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>

plugin/errors/benchmark_test.go

@@ -18,7 +18,7 @@ func BenchmarkServeDNS(b *testing.B) {
 	w := &test.ResponseWriter{}
 	ctx := context.TODO()
 
-	for i := 0; i < b.N; i++ {
+	for range b.N {
 		_, err := h.ServeDNS(ctx, w, r)
 		if err != nil {
 			b.Errorf("ServeDNS returned error: %s", err)