[FW][MERGE] base,note,snailmail: perf of users and partners create/write

Following the new populate functionality (populating the database with generated records),
this PR aims to improve:

* the creation of users (missed batching opportunity)
* the update of partners (optimized write to potentially reduce database requests).

Followup of #48912
Task Id - 2229358

closes odoo/odoo#50452

Forward-port-of: odoo/odoo#50367
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>
Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>