* Don't vote for empty leader transmissions
* Add is_delta flag to bank to detect empty leader transmissions
* Plumb new is_votable flag through replay stage
* Fix PohRecorder tests
* Change is_delta to AtomicBool to avoid making Bank references mutable
* Reset start slot in poh_recorder when working bank is cleared, so that connsecutive TPU's will start from the correct place
* Use proper max tick height calculation
* Test for not voting on empty transmission
* tests for is_votable
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