chore(all): move sub-packages to internal/provider

internal/provider/nordvpn/updater/ip.go

@@ -0,0 +1,16 @@
+package nordvpn
+
+import (
+	"fmt"
+	"net"
+)
+
+func parseIPv4(s string) (ipv4 net.IP, err error) {
+	ip := net.ParseIP(s)
+	if ip == nil {
+		return nil, fmt.Errorf("%w: %q", ErrParseIP, s)
+	} else if ip.To4() == nil {
+		return nil, fmt.Errorf("%w: %s", ErrNotIPv4, ip)
+	}
+	return ip, nil
+}