Various improvements (#461)

* **New Features**
  * Time and delay utilities added (ticks, ms, µs); SD card now uses an expansion-header CS pin; HTTP downloads warn when run on the GUI task and yield to avoid blocking.

* **Bug Fixes / Reliability**
  * Many hard-crash paths converted to guarded checks to reduce abrupt termination and improve stability.

* **Tests**
  * Unit tests added to validate time and delay accuracy.

* **Chores**
  * License header and build/macro updates.

TactilityKernel/Include/Tactility/Delay.h

@@ -0,0 +1,54 @@
+#pragma once
+
+#include "Time.h"
+#include <stdint.h>
+
+#ifdef ESP_PLATFORM
+#include <rom/ets_sys.h>
+#else
+#include <unistd.h>
+#endif
+
+#include <Tactility/Check.h>
+#include "Tactility/FreeRTOS/FreeRTOS.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Delay the current task for the specified amount of ticks
+ * @warning Does not work in ISR context
+ */
+static inline void delay_ticks(TickType_t ticks) {
+    check(xPortInIsrContext() == pdFALSE);
+    if (ticks == 0U) {
+        taskYIELD();
+    } else {
+        vTaskDelay(ticks);
+    }
+}
+
+/**
+ * Delay the current task for the specified amount of milliseconds
+ * @warning Does not work in ISR context
+ */
+static inline void delay_millis(uint32_t milliSeconds) {
+    delay_ticks(millis_to_ticks(milliSeconds));
+}
+
+/**
+ * Stall the currently active CPU core for the specified amount of microseconds.
+ * This does not allow other tasks to run on the stalled CPU core.
+ */
+static inline void delay_micros(uint32_t microseconds) {
+#ifdef ESP_PLATFORM
+    ets_delay_us(microseconds);
+#else
+    usleep(microseconds);
+#endif
+}
+
+#ifdef __cplusplus
+}
+#endif