This update adjusts the Time Off module's testing setup to use shared test assets. It helps keep automated tests more consistent and easier to maintain, with no expected change for everyday users.

task-2411138

The Mail app now uses shared stored data to track which message is selected, instead of passing that detail through multiple screen components. This makes message selection behavior more consistent and easier to maintain, with minimal visible change for users.

task-2282218

The Documents app test setup now uses shared test assets in a more consistent way. This is an internal quality improvement that helps keep automated tests easier to maintain without changing how users work with documents.

task-2411138

Deletion safeguards were moved to a safer standard mechanism across several Odoo apps. This helps keep business rules consistent when records are removed, reducing the risk of accidental data issues without changing day-to-day workflows.

With this commit, all instances of errors being raised inside
`BaseModel.unlink` overrides are moved into methods decorated with
`api.ondelete` which is safer.

Linked to https://github.com/odoo/odoo/pull/58517