update target_max_lum_nits from LedSettingsBaseModel itself

[DevTGHa]

Control target_max_lum_nits from LedSettingsBaseModel itself

Summary

For OpenVPCal application, this is duplicated process because LedWallSettings's @property setter has a logic to handle this.
However, the colour calibration plugin use LedSettingsBaseModel instead of LedWallSettings to manage data, it'd be very handy to have this model_validator so target_max_lum_nits can get updated based on target_eotf.

I understand this can be controversial, so I'll back out it this is not desired change.

[davisadam10]

So I think this is where we need to do some kind of cleanup/refactor.

We have moved over to use a pydantic but we have it kinda wrapped that.

I think we would be better to do some more work here, so that we have a single class which we all set and get rather than spreading setters and getters throughout the project.

My 2 cents is lets talk in the new year and we can probably figure out how to make this cleaner.

I'd rather put the effort into revisting the pydantic implementation.