fix clock drift for assignments issued before the block (#3851)

* fix clock drift for assignments issued before the block

* always broadcast tranche 0 assignments

* Update tests

* Change from min to max

* Remove erronious print statement

* guide: require fixed approval delay

* prevent approval by very recent assignments

* fix approval-checking tests

* fix main approval tests

* Fix tests

* Fix looked over test

* fix test

Co-authored-by: Lldenaurois <[email protected]>