[FIX] hr_holidays: Rounding allocation_used_count and allocation_count

Steps to reproduce the bug:

- Let's consider an employee E with 8.00 hours as Average Hour per Day
- Create an Allocation for E with a Time-off Type in Hours
(be sure the number of hours is different from the average hour per Day)
- Open the form view of E

Bug:

The smart button Time Off(remaining leaves) was completely unreadable

opw:2441019

closes odoo/odoo#66760

Signed-off-by: Simon Goffin (sig) <sig@openerp.com>