Maintenance: refactor servers updater code

- Require at least 80% of number of servers now to pass
- Each provider is in its own package with a common structure
- Unzip package with unzipper interface
- Openvpn package with extraction and download functions

internal/updater/providers/torguard/filename.go

@@ -0,0 +1,31 @@
+package torguard
+
+import "strings"
+
+func parseFilename(fileName string) (country, city string) {
+	const prefix = "TorGuard."
+	const suffix = ".ovpn"
+	s := strings.TrimPrefix(fileName, prefix)
+	s = strings.TrimSuffix(s, suffix)
+
+	switch {
+	case strings.Count(s, ".") == 1 && !strings.HasPrefix(s, "USA"):
+		parts := strings.Split(s, ".")
+		country = parts[0]
+		city = parts[1]
+
+	case strings.HasPrefix(s, "USA"):
+		country = "USA"
+		s = strings.TrimPrefix(s, "USA-")
+		s = strings.ReplaceAll(s, "-", " ")
+		s = strings.ReplaceAll(s, ".", " ")
+		s = strings.ToLower(s)
+		s = strings.Title(s)
+		city = s
+
+	default:
+		country = s
+	}
+
+	return country, city
+}