Ensure we don't construct finalize votes for rounds we have timed out on

[samliok]

https://github.com/ava-labs/Simplex/blob/main/epoch.go#L1021

we never check if we have timed out on a round before re-constructing a finalize vote message

[yacovm]

we can send a finalize vote if we have finalized a descendant.