Refactor: A faster DomainMatcher implementation (#348)

Co-authored-by: DarthVader <61409963+darsvador@users.noreply.github.com>

app/dns/server.go

@@ -348,7 +348,6 @@ func (s *Server) LookupIP(domain string, option dns.IPOption) ([]net.IP, error)
 	if domain == "" {
 		return nil, newError("empty domain name")
 	}
-	domain = strings.ToLower(domain)
 
 	// normalize the FQDN form query
 	if strings.HasSuffix(domain, ".") {