chore(all): provider to servers map in allServers

- Simplify formatting CLI
- Simplify updater code
- Simplify filter choices for config validation
- Simplify all servers deep copying
- Custom JSON marshaling methods for `AllServers`
- Simplify provider constructor switch
- Simplify storage merging
- Simplify storage reading and extraction
- Simplify updating code

internal/storage/sync.go

@@ -7,27 +7,11 @@ import (
 	"github.com/qdm12/gluetun/internal/models"
 )
 
-func countServers(allServers models.AllServers) int {
-	return len(allServers.Cyberghost.Servers) +
-		len(allServers.Expressvpn.Servers) +
-		len(allServers.Fastestvpn.Servers) +
-		len(allServers.HideMyAss.Servers) +
-		len(allServers.Ipvanish.Servers) +
-		len(allServers.Ivpn.Servers) +
-		len(allServers.Mullvad.Servers) +
-		len(allServers.Nordvpn.Servers) +
-		len(allServers.Perfectprivacy.Servers) +
-		len(allServers.Privado.Servers) +
-		len(allServers.Pia.Servers) +
-		len(allServers.Privatevpn.Servers) +
-		len(allServers.Protonvpn.Servers) +
-		len(allServers.Purevpn.Servers) +
-		len(allServers.Surfshark.Servers) +
-		len(allServers.Torguard.Servers) +
-		len(allServers.VPNUnlimited.Servers) +
-		len(allServers.Vyprvpn.Servers) +
-		len(allServers.Wevpn.Servers) +
-		len(allServers.Windscribe.Servers)
+func countServers(allServers models.AllServers) (count int) {
+	for _, servers := range allServers.ProviderToServers {
+		count += len(servers.Servers)
+	}
+	return count
 }
 
 func (s *Storage) SyncServers() (err error) {
@@ -57,7 +41,7 @@ func (s *Storage) SyncServers() (err error) {
 		return nil
 	}
 
-	if err := flushToFile(s.filepath, s.mergedServers); err != nil {
+	if err := flushToFile(s.filepath, &s.mergedServers); err != nil {
 		return fmt.Errorf("cannot write servers to file: %w", err)
 	}
 	return nil