[IMP]HR_HOLIDAY:In employee form view in rename Approved Leaves oe_stat ...

...button into Leaves to process also add a TO Do filter and rename Number Of Leaves into Remaining Leaves oe_stat button and all group visible by employee ,add a filter type and year. also change a oe_stat button on number of leaves.
https://www.odoo.com/web?#id=10204&view_type=form&model=project.task&action=327
pad: https://pad.odoo.com/p/r.2FBjWajDmTJjrTiC
I think, you should use read_group : group_by 'type', sum **number_of_days_temp**
sum(res['add'] - res['remove'])