Add connection check for W5500 before full initialization

include/W5500.h

@@ -2,19 +2,28 @@
 #pragma once
 
 #include <Arduino.h>
+#include <driver/spi_master.h>
 #include <esp_eth.h> // required for esp_eth_handle_t
 #include <esp_netif.h>
 
+#include <memory>
+
 class W5500 {
+private:
+    explicit W5500(spi_device_handle_t spi, gpio_num_t pin_int);
+
 public:
-    explicit W5500(int8_t pin_mosi, int8_t pin_miso, int8_t pin_sclk, int8_t pin_cs, int8_t pin_int, int8_t pin_rst);
     W5500(const W5500&) = delete;
     W5500& operator=(const W5500&) = delete;
     ~W5500();
 
+    static std::unique_ptr<W5500> setup(int8_t pin_mosi, int8_t pin_miso, int8_t pin_sclk, int8_t pin_cs, int8_t pin_int, int8_t pin_rst);
     String macAddress();
 
 private:
+    static bool connection_check_spi(spi_device_handle_t spi);
+    static bool connection_check_interrupt(gpio_num_t pin_int);
+
     esp_eth_handle_t eth_handle;
     esp_netif_t* eth_netif;
 };