[FIX] mrp{_account}: consider capacities when computing duration

Related enterprise PR: odoo/enterprise#39669

Steps to reproduce:

Install mrp_workorder
Create Product P1, Workcenter W1
Edit W1 > Specific capacities > Add line: Product = P1, Start time = 5, End time = 5
Create BoM > Product: P1, Operations tab > Add line: Workcenter = WC1, Default duration = 60:00 min > Save
Click on overview stat button
Issue:

The created operation has expected time of 60:00, instead of 70:00. The workcenter start and stop times are considered in this calculation, so the workcenter capacities should be considered too.

Solution:

Use `_get_expected_duration` to compute the expected duration.

opw-3229485

closes odoo/odoo#118360

Signed-off-by: Tiffany Chang <tic@odoo.com>