Update counters now that all changes in this PR are validated.
Main observations
* batch mode is improved: few tests effectively run on a real batch of
records but in those use cases there are more gains due to better batch
management of values rendering and recipients management;
* posting using a view does not call the composer anymore in all situations
allowing to gain a lot of queries by not creating a composer and calling
a dummy onchange on it;
* various small gains in various tests, notably linked to usage of low-level
reference fetch and various small code tweaks;
Task-2710804 (Mail: Clean MailThread API)
Part-of: odoo/odoo#99482