cfg: more precise check for replication_synchro_quorum value

When we fetch replication_synchro_quorum value (either as
a plain integer or via formula evaluation) we trim the
number down to integer, which silently hides potential
overflow errors.

For example

 | box.cfg{replication_synchro_quorum='4294967297'}

which is 1 in terms of machine words. Lets use 8 bytes
values and trigger an error instead.

Part-of #5446

Reported-by: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>