Pull request: use mathutil

Merge in DNS/adguard-home from use-mathutil to master

Squashed commit of the following:

commit cfe2c02a7bb727e81fcd91674aa777df37413a8e
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Tue Jan 24 18:12:32 2023 +0300

    all: use mathutil

internal/home/authratelimiter.go

@@ -66,11 +66,12 @@ func (ab *authRateLimiter) check(usrID string) (left time.Duration) {
 	defer ab.failedAuthsLock.Unlock()
 
 	ab.cleanupLocked(now)
+
 	return ab.checkLocked(usrID, now)
 }
 
 // incLocked increments the number of unsuccessful attempts for attempter with
-// ip and updates it's blocking moment if needed.  For internal use only.
+// usrID and updates it's blocking moment if needed.  For internal use only.
 func (ab *authRateLimiter) incLocked(usrID string, now time.Time) {
 	until := now.Add(failedAuthTTL)
 	var attNum uint = 1