[FIX] product: fix contained quantity decimal precision

Steps to reproduce the bug:
- Activate packaging in inventory configurations
- set the product UOM digits to more than 2 decimals
- Create a storable product:
    - Go to inventory tab > Packaging > Add a line
    - Change the contained quantity to a value with more than 2 decimal places

Problem:
It will round it to 2 decimal places regardless of the set digits.
Because the formatFloat function does not receive the digits in parameter, so it uses 2 as default value

Problem:

opw-2723068

closes odoo/odoo#83368

X-original-commit: 28f87fa6
Signed-off-by: William Henrotin (whe) <whe@odoo.com>
Signed-off-by: Djamel Touati (otd) <otd@odoo.com>