This makes use of the `periph_timer_query_freqs` feature:
1. It does choose the closest frequency supported before calling
timer_init() in the ztimer_periph_timer backend.
2. It does make use of the actually chosen frequency when using
`ztimer_convert_frac`.
3. It does `assert()` the frequency is within 5% of the specified when
no frequency conversion is performed or `ztimer_convert_shift_up`
is used.
