Do not set effective date on assignation
Currently the assignation process set an effective date to today to ensure that the quantity is reserved for now and any future request.
But the drawback is that assigned move can not stay longer as the day because the effective date will be in the past and the stock quantity computation will ignore it.
So a solution if we want to allow longer assignation is to not set the effective date on assigned move but to get the stock quantity computation always add assigned moves when stock_assign is set.
This behaviour can only be done when computing the stock quantity for a specific date. When it is delta computing we must follow the effective/planned date.