The WhatsApp integration now uses a standard internal process to update chat participant data. This is a behind-the-scenes cleanup that should make the messaging code easier to maintain without changing the user experience.

community PR: https://github.com/odoo/odoo/pull/232615

This commit refactors the `discuss.channel.member/fetched` bus notification to be a `mail.record/insert` as there is no other logic than inserting channel member data in the store.

task-5177252

This change moves Odoo's internal test add-ons into a dedicated tests subdirectory. It does not change business features, but it makes the codebase easier to maintain and helps development teams manage testing assets more clearly.

Same as community but a different variant as all addons live at the toplevel of the repo: test addons are moved to a subdirectory.