Pull request: all: imp code, decr cyclo

Updates #2646.

Squashed commit of the following:

commit c83c230f3d2c542d7b1a4bc0e1c503d5bbc16cb8
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Mar 25 19:47:11 2021 +0300

    all: imp code, decr cyclo

internal/dnsforward/dnsforward_test.go

@@ -632,7 +632,7 @@ func TestClientRulesForCNAMEMatching(t *testing.T) {
 		TCPListenAddrs: []*net.TCPAddr{{}},
 		FilteringConfig: FilteringConfig{
 			ProtectionEnabled: true,
-			FilterHandler: func(_ net.IP, _ string, settings *dnsfilter.RequestFilteringSettings) {
+			FilterHandler: func(_ net.IP, _ string, settings *dnsfilter.FilteringSettings) {
 				settings.FilteringEnabled = false
 			},
 		},