[flexiglass] Always round up the remaining throttle milliseconds.

This fixes a bug where we show the user there are 0 seconds remaining
before they can try to re-authenticate during throttling.

Bonus: since we only store this value in the model for presenting it to
the user, we should store it in seconds directly rather than converting
from milliseconds when formatting the message (which happens every
second during throttling).

Fix: 314308690
Bug: 314757822
Test: Unit tests updated and still pass.
Flag: ACONFIG com.android.systemui.scene_container DEVELOPMENT
Change-Id: Ifbf4708b687c037877784b29427c56ee2f20ab37