Add Phase 0 RS-232 characterization harness and test firmware with cli

src/status_led.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "esp_err.h"
+
+typedef enum {
+    STATUS_LED_IDLE,
+    STATUS_LED_RUNNING,
+    STATUS_LED_PASS,
+    STATUS_LED_FAIL,
+} status_led_state_t;
+
+esp_err_t status_led_init(void);
+esp_err_t status_led_set(status_led_state_t state);