Add unit tests for buttons / relays; and a bunch of mocks :)

unittest/mgos_mock.c

@@ -50,6 +50,26 @@ void mgos_clear_timer(mgos_timer_id id) {
   return;
 }
 
-float mg_time() {
+double mg_time() {
   return (float) time(NULL);
 }
+
+double mgos_uptime() {
+  return (double) time(NULL);
+}
+
+char *mgos_sys_ro_vars_get_mac_address() {
+  return "00:11:22:33:44:55";
+}
+
+char *mgos_sys_ro_vars_get_arch() {
+  return "esp32";
+}
+
+bool mgos_net_get_ip_info(enum mgos_net_if_type if_type, int if_instance, struct mgos_net_ip_info *ip_info) {
+  return true;
+}
+
+void mgos_net_ip_to_str(const struct sockaddr_in *sin, char *out) {
+  return;
+}