[FIX] stock: fix rounding issue on available quantity

- Have a storable product with 3140.0 quantity on hand
- Make a sale order for 3106.40, confirm and validate delivery
- Reserved quantity will be 3106.40
- Make another sale order for 33.60, confirm and go to delivery
- Reserved quantity will be 33.59 because of a rounding issue when
calculating the available quantity

opw-2449732

closes odoo/odoo#65453

Signed-off-by: agr-odoo <agr-odoo@users.noreply.github.com>