Stock product quantity views now rely on a standard computed value instead of special internal context options. This reduces maintenance complexity and helps keep inventory quantities consistent across product screens.

This change updates rental stock logic to use the standard valued-quantity field instead of a special context flag. It reduces internal complexity and helps keep rental inventory valuation behavior aligned with the rest of Odoo.

The correct way to get what quantities are valued is to used the
`quantity_svl` computed field.