Bootloader Programmer Application

Currently, when a new dispenser is added to the system, a model number is assigned and then it becomes fixed.

However, we need a change in this behavior based on the serial number:

There are default serial numbers for DU and DISPLAY (9900000 and 12000000) respectively.
For these default serial numbers, the system should allow multiple model numbers to be assigned.
For all other serial numbers (non-default serial numbers), the system should allow only one model number to be assigned.

Expected Behavior:

If the dispenser has a default serial number (9900000 and 12000000) → multiple models can be selected/assigned.
If the dispenser has any other serial number → only a single model should be allowed, and it should remain fixed once assigned.

This change is required so that default serial numbers can be used for testing or flexible configuration, while real serial numbers remain restricted to a single model.