Fixes #5690

The problem: we accessed the caller stack variables (max_exec_cycles) in MultiCommandSquasher::ExecuteSquashed.
The access was done after the call to `bc.Dec()`, which unblocks ExecuteSquashed.
As a result, the callback function that was still running could corrupt memory contents of some other variable
as ExecuteSquashed could exit by that time.

In addition, harden checks in stream_family.cc in StreamAppendItem.
Finally, we update helio which fixes #5693

Signed-off-by: Roman Gershman <roman@dragonflydb.io>