* Unit tests update, code cosmetics
* Fix segfault with zombie handling
why:
In order to save memory, the data records of zombie entries are removed
and only the key (aka peer node) is kept. Consequently, logging these
zombies can only be done by the key.
* Allow to accept V2 payload without `shanghaiTime` set while syncing
why:
Currently, `shanghaiTime` is missing (alt least) while snap syncing. So
beacon node headers can be processed regardless. Normal (aka strict)
processing will be automatically restored when leaving snap sync mode.
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