[FIX] mrp: use product unit of measure precision in BoM overview

Steps to reproduce the bug:
- Go to Decimal accuracy:
    - Select the “Product Unit of Measure”
    - Set the Value to “4”

- Create a storable product with BoM:
    - add any product as component
    - save
    - Click on the BoM overview widget

Problem:
The “Product UoM” precision is not used

opw-3288403

closes odoo/odoo#120079

Signed-off-by: William Henrotin (whe) <whe@odoo.com>