fix indivisible reduction periods warning

[haakon-e]

As far as I can tell, #3396 implemented the warning for indivisible frequencies incorrectly.

e.g., if

periods_reductions = Set([Dates.Second(3600)])  # every hour
checkpoint_frequency = Dates.Millisecond(1800000)  # every 30 minutes, i.e. the value of dt_save_state_to_disk

I currently get the warning: Warning: Some accumulated diagnostics might not be evenly divisible by the checkpointing frequency (30 minutes)

but, unless I am misunderstanding what's going on here, this should be perfectly fine.

---

This PR essentially reverses the order of the arguments to CA.isdivisible so that we now have:

if any(
    x -> !CA.isdivisible(x, checkpoint_frequency),
    periods_reductions,
)
    accum_str = join(CA.promote_period.(collect(periods_reductions)), ", ")
    checkpt_str = CA.promote_period(checkpoint_frequency)
    @warn "Diagnostics are accumulated at frequencies ($accum_str), which may not be evenly divisible by the checkpointing frequency (dt_save_state_to_disk = $checkpt_str)"
end

[Sbozzolo]

I think the warning is correct: if you have hourly diagnostics, but checkpoints every 30 minutes, you could restart the simulation from an invalid state if you restart from odd checkpoints.

[haakon-e]

I see. So I did indeed misunderstand it then. I think I got caught up in the phrasing

Some accumulated diagnostics might not be evenly divisible by the checkpointing frequency

suggesting that we check if (accumulated diagnostics) / (checkpointing frequency) is an integer, but we actually do the opposite.

[Sbozzolo]

I think you are right. Feel free to flip the phrasing in this PR.

[haakon-e]

something like this?

"The checkpointing frequency (dt_save_state_to_disk = $checkpt_str) should be an integer multiple of all diagnostics accumulation periods ($accum_str) to simulations can be safely restarted from any checkpoint"