chore(all): return concrete types, accept interfaces

- Remove exported interfaces unused locally
- Define interfaces to accept arguments
- Return concrete types, not interfaces

internal/vpn/openvpn.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 
 	"github.com/qdm12/gluetun/internal/configuration/settings"
-	"github.com/qdm12/gluetun/internal/firewall"
 	"github.com/qdm12/gluetun/internal/openvpn"
 	"github.com/qdm12/gluetun/internal/provider"
 	"github.com/qdm12/golibs/command"
@@ -13,10 +12,10 @@ import (
 
 // setupOpenVPN sets OpenVPN up using the configurators and settings given.
 // It returns a serverName for port forwarding (PIA) and an error if it fails.
-func setupOpenVPN(ctx context.Context, fw firewall.VPNConnectionSetter,
-	openvpnConf openvpn.Interface, providerConf provider.Provider,
+func setupOpenVPN(ctx context.Context, fw Firewall,
+	openvpnConf OpenVPN, providerConf provider.Provider,
 	settings settings.VPN, starter command.Starter, logger openvpn.Logger) (
-	runner vpnRunner, serverName string, err error) {
+	runner *openvpn.Runner, serverName string, err error) {
 	connection, err := providerConf.GetConnection(settings.Provider.ServerSelection)
 	if err != nil {
 		return nil, "", fmt.Errorf("failed finding a valid server connection: %w", err)