Floor instead of round in speaker/projector countdown

[hjanott]

Rounding can lead to missing seconds in the countdown when its paused and restarted. Instead the speaker should be granted the extra fractions of a second.
An example of such flattery behaviour can be found here. https://github.com/OpenSlides/openslides-backend/actions/runs/22442431027/job/64988037872?pr=3370
Another solution would be to store milliseconds instead of seconds.

[luisa-beerboom]

Considering that these speaking times are often connected to the user organizations statutes I'd prefer them to be as accurate as possible. If some concessions need to be made I strongly believe we should make the speaking time shorter rather than longer