The tests used to measure the throughput by FreeRTOS
`xTaskGetTickCount()`. The rounding error can be quite big, compared to
total measurement time (1350 ms for 4-bit mode).
This commit use `esp_timer_get_time()` instead to measure typical time,
which is in microseconds. Moreover, to get rid of the time error from
cache miss, `ccomp_timer_*` are used to get the cache compensated time
to measure the throughput used for unit test performance assertion.
69d9e0eadc