[FIX] mail : speed systray_get_activities
When the number of mail.activities for a user was getting too big, the whole database is getting slowed down as the activities are recomputed each time a page is loaded. The issue was mostly brought by commit [03c3d440](https://github.com/odoo/odoo/commit/03c3d440ae31baa0400b7adba7f6373556ff5c38 ). The time was recorded when refreshing the home page of the site. | | | | | --- | --- | --- | | #activities | before PR | after PR | | 100 000 on 1 model | 22.66s (single test) | 0.408s (worst of few runs) | | 40 on 40 models | 0.06s worst, 0.037s best | 0.053s (worst of few) (0.038s best) | closes odoo/odoo#134126 Signed-off-by:Sébastien Theys (seb) <seb@odoo.com>