[MERGE] crm: fix randomly failing tests about query counters and assign domain

PURPOSE

Fix recently added lead assignment tests, notably about query counters
and random behavior of lead merge.

SPECIFICATIONS

Split performance tests from unit tests. Performance tests should be
reproducible. Currently there are too much varying query counters.

Fix lead merge process done during assign. As duplicate leads are merged
final opportunity could not fit team domain anymore. This is a side effect
of lead deduplication. In this case this is linked to priority field that is set
to the value of the "final" opportunity, whatever the value of other leads
merged into it. We think that priority is a field that should be managed
more carefully. We choose to set it as the highest value found in leads
merged.

LINKS

Task ID-2446759 (lead merge priority field management)
Task ID-2446883 (query counters fix)
PR odoo/odoo#65016

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>