Since the computation of employees work intervals is done in batch,
i.e. 1 call to _work_intervals for each (tz, resource_calendar_id) pairs,
removing tz duplicates from mapped results improves
the perf of hr_presence_state/hr_icon_display computations.
This is especially true for grouped hr.employee kanban view as each column
search_read triggers a recompute for these fields.
closesodoo/odoo#71772
X-original-commit: be6d4a2523bb1a292908d09dfc5393bc0aa88a2d
Signed-off-by: Kevin Baptiste <kba@odoo.com>