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/concurrent/Mutex.h

@@ -4,6 +4,8 @@
 
 #include <assert.h>
 #include <stdbool.h>
+
+#include <Tactility/Check.h>
 #include <Tactility/FreeRTOS/semphr.h>
 
 #ifdef __cplusplus
@@ -28,17 +30,17 @@ inline static void mutex_destruct(struct Mutex* mutex) {
 }
 
 inline static void mutex_lock(struct Mutex* mutex) {
-    assert(xPortInIsrContext() != pdTRUE);
+    check(xPortInIsrContext() != pdTRUE);
     xSemaphoreTake(mutex->handle, portMAX_DELAY);
 }
 
 inline static bool mutex_try_lock(struct Mutex* mutex) {
-    assert(xPortInIsrContext() != pdTRUE);
+    check(xPortInIsrContext() != pdTRUE);
     return xSemaphoreTake(mutex->handle, 0) == pdTRUE;
 }
 
 inline static bool mutex_try_lock_timed(struct Mutex* mutex, TickType_t timeout) {
-    assert(xPortInIsrContext() != pdTRUE);
+    check(xPortInIsrContext() != pdTRUE);
     return xSemaphoreTake(mutex->handle, timeout) == pdTRUE;
 }
 
@@ -51,7 +53,7 @@ inline static bool mutex_is_locked(struct Mutex* mutex) {
 }
 
 inline static void mutex_unlock(struct Mutex* mutex) {
-    assert(xPortInIsrContext() != pdTRUE);
+    check(xPortInIsrContext() != pdTRUE);
     xSemaphoreGive(mutex->handle);
 }