[FIX] account: do not use optional library
[FIX] account: do not use optional library

stdnum is not a mandatory dependency
It is often present as required to install the base_vat module but
having a system with account without the dependency should be
possible.

As the calc_check_digits is pretty small, it is easy to extract

Forward port of 6091be6556d to 13.0

closes odoo/odoo#40265

X-original-commit: ef245e14730e5c4858b81adfbe7e309631688663
Signed-off-by: Martin Trigaux (mat) <cc7c5be316e48d137cbb549833b85d91034d799d@odoo.com>

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo