Faster servers information updater (#248)

* Asynchronous repeatResolve
* Parallel cyberghost and PIA (v3) processing, with a 10 goroutines limit
* Add missing vyprvpn cli flag to updater
* Increase DNS repetitions to 5 in order to obtain more IP addresses
* Update old PIA IP addresses
* Add Surfshark servers by API (unused for now)

internal/updater/windscribe.go

@@ -31,7 +31,8 @@ func findWindscribeServers(ctx context.Context, lookupIP lookupIPFunc) (servers
 			return nil, err
 		}
 		host := countryCode + "." + domain
-		ips, err := resolveRepeat(ctx, lookupIP, host, 2)
+		const repetitions = 5
+		ips, err := resolveRepeat(ctx, lookupIP, host, repetitions)
 		if err != nil || len(ips) == 0 {
 			continue
 		}