Use built-in alsoPropagate mechanism that wraps commands
in MULTI/EXEC before sending them to replica/AOF

in some cases we were trying to kill the fork before it got created

it seems that running two clients at a time is ok too, resuces action
time from 20 minutes to 10. we'll use this for now, and if one day it
won't be enough we'll have to run just the sensitive tests one by one
separately from the others.

this commit also fixes an issue with the defrag test that appears to be
very rare.

seems that github actions are slow, using just one client to reduce
false positives.

also adding verbose, testing only on latest ubuntu, and building on
older one.

when doing that, i can reduce the test threshold back to something saner

I saw that the new defag test for list was failing in CI recently, so i
reduce it's threshold from 12 to 60.

besides that, i add / improve the latency test for that other two defrag
tests (add a sensitive latency and digest / save checks)

and fix bad usage of debug populate (can't overrides existing keys).
this was the original intention, which creates higher fragmentation.

When active defrag kicks in and finds a big list, it will create a bookmark to
a node so that it is able to resume iteration from that node later.

The quicklist manages that bookmark, and updates it in case that node is deleted.

This will increase memory usage only on lists of over 1000 (see
active-defrag-max-scan-fields) quicklist nodes (1000 ziplists, not 1000 items)
by 16 bytes.

In 32 bit build, this change reduces the maximum effective config of
list-compress-depth and list-max-ziplist-size (from 32767 to 8191)

... with CSC disabled

This fixes WATCH and client side caching with keys expiring because of
a synchronous access and not because of background expiring.