Persistent server pools (#226)

* GetAllServers with version & timestamp tests
* Storage package to sync servers
* Use storage Sync to get and use servers

internal/models/server.go

@@ -0,0 +1,52 @@
+package models
+
+import "net"
+
+type PIAServer struct {
+	IPs    []net.IP `json:"ips"`
+	Region string   `json:"region"`
+}
+
+type MullvadServer struct {
+	IPs     []net.IP `json:"ips"`
+	Country string   `json:"country"`
+	City    string   `json:"city"`
+	ISP     string   `json:"isp"`
+	Owned   bool     `json:"owned"`
+}
+
+type WindscribeServer struct {
+	Region string   `json:"region"`
+	IPs    []net.IP `json:"ips"`
+}
+
+type SurfsharkServer struct {
+	Region string   `json:"region"`
+	IPs    []net.IP `json:"ips"`
+}
+
+type CyberghostServer struct {
+	Region string   `json:"region"`
+	Group  string   `json:"group"`
+	IPs    []net.IP `json:"ips"`
+}
+
+type VyprvpnServer struct {
+	Region string   `json:"region"`
+	IPs    []net.IP `json:"ips"`
+}
+
+type NordvpnServer struct { //nolint:maligned
+	Region string `json:"region"`
+	Number uint16 `json:"number"`
+	IP     net.IP `json:"ip"`
+	TCP    bool   `json:"tcp"`
+	UDP    bool   `json:"udp"`
+}
+
+type PurevpnServer struct {
+	Region  string   `json:"region"`
+	Country string   `json:"country"`
+	City    string   `json:"city"`
+	IPs     []net.IP `json:"ips"`
+}