This is a fix for at least one cause of this isssue:
https://github.com/ledgerwatch/erigon/issues/8212.
It happens after the end of the snapshot load, because the snapshot
processing which was introduced a couple of month ago does not deal with
validation of the headers at the start of the start of the chain.
I have also added a fix to the persistence so that the last snapshot is
recorded so that subsequent runs are not forced to process the whole
snapshot run from start.
The relationship between this an memory usage is that the fact that
headers are not processed leads to a queue of pending headers with size
of around 5GB. I have not changed any header parameters - so likely a
prolonged stop to header processing will result in a similar level of
memory growth.
