cherry-pick: 4358 fix stats

Merge in DNS/adguard-home from 4358-fix-stats to master

Updates #4358.
Updates #4342.

Squashed commit of the following:

commit 5683cb304688ea639e5ba7f219a7bf12370211a4
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 4 18:20:54 2022 +0300

    stats: rm races test

commit 63dd67650ed64eaf9685b955a4fdf3c0067a7f8c
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 4 17:13:36 2022 +0300

    stats: try to imp test

commit 59a0f249fc00566872db62e362c87bc0c201b333
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 4 16:38:57 2022 +0300

    stats: fix nil ptr deref

commit 7fc3ff18a34a1d0e0fec3ca83a33f499ac752572
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Apr 7 16:02:51 2022 +0300

    stats: fix races finally, imp tests

commit c63f5f4e7929819fe79b3a1e392f6b91cd630846
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 4 00:56:49 2022 +0300

    aghhttp: add register func

commit 61adc7f0e95279c1b7f4a0c0af5ab387ee461411
Merge: edbdb2d4 9b3adac1
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Thu Aug 4 00:36:01 2022 +0300

    Merge branch 'master' into 4358-fix-stats

commit edbdb2d4c6a06dcbf8107a28c4c3a61ba394e907
Merge: a91e4d7a a481ff4c
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 3 21:00:42 2022 +0300

    Merge branch 'master' into 4358-fix-stats

commit a91e4d7af13591eeef45cb7980d1ebc1650a5cb7
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 3 18:46:19 2022 +0300

    stats: imp code, docs

commit c5f3814c5c1a734ca8ff6726cc9ffc1177a055cf
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 3 18:16:13 2022 +0300

    all: log changes

commit 5e6caafc771dddc4c6be07c34658de359106fbe5
Merge: 091ba756 eb8e8166
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 3 18:09:10 2022 +0300

    Merge branch 'master' into 4358-fix-stats

commit 091ba75618d3689b9c04f05431283417c8cc52f9
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Aug 3 18:07:39 2022 +0300

    stats: imp docs, code

commit f2b2de77ce5f0448d6df9232a614a3710f1e2e8a
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Aug 2 17:09:30 2022 +0300

    all: refactor stats & add mutexes

commit b3f11c455ceaa3738ec20eefc46f866ff36ed046
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Wed Apr 27 15:30:09 2022 +0300

    WIP

internal/dnsforward/config.go

@@ -5,12 +5,12 @@ import (
 	"crypto/x509"
 	"fmt"
 	"net"
-	"net/http"
 	"os"
 	"sort"
 	"strings"
 	"time"
 
+	"github.com/AdguardTeam/AdGuardHome/internal/aghhttp"
 	"github.com/AdguardTeam/AdGuardHome/internal/filtering"
 	"github.com/AdguardTeam/dnsproxy/proxy"
 	"github.com/AdguardTeam/dnsproxy/upstream"
@@ -191,7 +191,7 @@ type ServerConfig struct {
 	ConfigModified func()
 
 	// Register an HTTP handler
-	HTTPRegister func(string, string, func(http.ResponseWriter, *http.Request))
+	HTTPRegister aghhttp.RegisterFunc
 
 	// ResolveClients signals if the RDNS should resolve clients' addresses.
 	ResolveClients bool

internal/dnsforward/dnsforward.go

@@ -61,7 +61,7 @@ type Server struct {
 	dnsFilter  *filtering.DNSFilter  // DNS filter instance
 	dhcpServer dhcpd.ServerInterface // DHCP server instance (optional)
 	queryLog   querylog.QueryLog     // Query log instance
-	stats      stats.Stats
+	stats      stats.Interface
 	access     *accessCtx
 
 	// localDomainSuffix is the suffix used to detect internal hosts.  It
@@ -107,7 +107,7 @@ const defaultLocalDomainSuffix = "lan"
 // DNSCreateParams are parameters to create a new server.
 type DNSCreateParams struct {
 	DNSFilter   *filtering.DNSFilter
-	Stats       stats.Stats
+	Stats       stats.Interface
 	QueryLog    querylog.QueryLog
 	DHCPServer  dhcpd.ServerInterface
 	PrivateNets netutil.SubnetSet

internal/dnsforward/stats_test.go

@@ -34,7 +34,7 @@ func (l *testQueryLog) Add(p *querylog.AddParams) {
 type testStats struct {
 	// Stats is embedded here simply to make testStats a stats.Stats without
 	// actually implementing all methods.
-	stats.Stats
+	stats.Interface
 
 	lastEntry stats.Entry
 }