[19.0][FIX] mail_tracking: don't flag co-recipients as error on a single bounce

[skanndar]

Problem

In the chatter, the "To:" line (the MessageTracking template added by mail_tracking) marks a red ✖ error on every recipient when a message goes to several and only one bounces — as if nobody received it. Recipients without a tracking record show unknown. Core's own envelope icon / MessageNotificationPopover show the correct per-recipient status; only the mail_tracking line is wrong.

Root cause

mail.tracking.email tracks per SMTP send, not per recipient. When a message goes to several recipients and the DSN of one bounces, the bounce state (soft-bounced/bounced) is shared by the co-recipients' mail.tracking.email, so mail.message.tracking_status() returns status='error' for recipients that were actually delivered; recipients with no tracking fall to 'unknown'.

Fix

The core mail.notification is per recipient and reliable, so reconcile the per-send tracking status against it at the end of tracking_status():

• core sent + tracking error/unknown → sent
• core bounce/exception + tracking sent/unknown/waiting → error
• delivered/opened (tracking-pixel info the core doesn't have) are left untouched.

Tests / reproduction

Regression test (test_corecipient_bounce.py) builds the real case: a message to four recipients, one really bounced (core bounce + tracking soft-bounced), two delivered but sharing the soft-bounced tracking, one delivered with no tracking. Verified A/B on odoo:19: before → all four error/unknown; after → only the real bounce is error, the other three sent.

Real-world sighting: a message to four recipients where one address did not exist (550 5.1.1 User unknown) showed all four as ✖.