The IoT driver code now treats each device identifier as a stable value rather than recalculating or passing it around in multiple places. This internal cleanup reduces inconsistency risk and helps keep IoT device communication and setup more reliable without changing user-facing behavior.

As the IoT identifier is a serial number or a motherboard uuid, it is not meant to change.
It then makes more sense for it to be a constant as `IS_WINDOWS` or `IS_LINUX` are.

Enterprise PR: odoo/enterprise#96549
Task: 5149362

The Belgian POS blackbox integration now uses a shared identifier value for IoT Box detection instead of recalculating it through an internal method. This is an internal cleanup that improves consistency and maintainability without changing the user experience.

We now use a constant instead of a call to a cached method to get the identifier of the IoT Box.
We updated the driver to use this constant.

Community PR: odoo/odoo#230346
Task: 5149362