zephyrCommon: Change delayMicroseconds to busy loop

Since Arduino's `delayMicroseconds` is implemented as a busy loop,
we change it to using `k_busy_wait` to improve compatibility.

Author: soburi

cores/arduino/zephyrCommon.cpp

@@ -280,7 +280,9 @@ void noTone(pin_size_t pinNumber) {
 
 void delay(unsigned long ms) { k_sleep(K_MSEC(ms)); }
 
-void delayMicroseconds(unsigned int us) { k_sleep(K_USEC(us)); }
+void delayMicroseconds(unsigned int us) {
+  k_busy_wait(us);
+}
 
 unsigned long micros(void) {
   return k_cyc_to_us_floor32(k_cycle_get_32());