The method orderpoint._compute_qty_order_computed was batched in commit 17a2de91afc7d879f95fe8210437ff6015af5585 then reverted in commit a58b99509a45a4372aca460eba22893f3358139e because of a bug introduced when purchase_stock is installed.

It should still be beneficial performance-wise to batch the calls to orderpoint._quantity_in_progress so this commit reintroduces the batching. The part that led to the issue was the override of _quantity_in_progress in the purchase_stock module. The first line
`self.product_id._get_quantity_in_progress(self.location_id.ids)` is not correctly working when len(self) > 1. So this method is not batchable in its current state.

To fix this, we inline it inside the for loop to retrieve the quantity_in_progress independently for each orderpoint in self. Thanks to that, the test introduced in 606dc7187a5 is passing even with the batched version of _compute_qty_to_order_computed.


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