[IMP] gamification: improve performance of ranks

Purpose
=======
Avoid calling _recompute_rank for users that are not affected by the
newly created/written ranks, by filtering users by karma_min

Task-2746929

closes odoo/odoo#89463

X-original-commit: 3a0562ea
Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>