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/mullvad/hosttoserver.go

@@ -0,0 +1,58 @@
+package mullvad
+
+import (
+	"errors"
+	"fmt"
+	"net"
+	"strings"
+
+	"github.com/qdm12/gluetun/internal/models"
+)
+
+type hostToServer map[string]models.MullvadServer
+
+var (
+	ErrParseIPv4 = errors.New("cannot parse IPv4 address")
+	ErrParseIPv6 = errors.New("cannot parse IPv6 address")
+)
+
+func (hts hostToServer) add(data serverData) (err error) {
+	if !data.Active {
+		return
+	}
+
+	ipv4 := net.ParseIP(data.IPv4)
+	if ipv4 == nil || ipv4.To4() == nil {
+		return fmt.Errorf("%w: %s", ErrParseIPv4, data.IPv4)
+	}
+
+	ipv6 := net.ParseIP(data.IPv6)
+	if ipv6 == nil || ipv6.To4() != nil {
+		return fmt.Errorf("%w: %s", ErrParseIPv6, data.IPv6)
+	}
+
+	server, ok := hts[data.Hostname]
+	if !ok {
+		server.Country = data.Country
+		server.City = strings.ReplaceAll(data.City, ",", "")
+		server.ISP = data.Provider
+		server.Owned = data.Owned
+	}
+
+	server.IPs = append(server.IPs, ipv4)
+	server.IPsV6 = append(server.IPsV6, ipv6)
+
+	hts[data.Hostname] = server
+
+	return nil
+}
+
+func (hts hostToServer) toServersSlice() (servers []models.MullvadServer) {
+	servers = make([]models.MullvadServer, 0, len(hts))
+	for _, server := range hts {
+		server.IPs = uniqueSortedIPs(server.IPs)
+		server.IPsV6 = uniqueSortedIPs(server.IPsV6)
+		servers = append(servers, server)
+	}
+	return servers
+}