this edit makes it so that ai toolkit can now accept user-defined optimizers such as schedule free and paged optimizers. - update optimizer.py

[Epispasm]

this edit makes it so that ai toolkit can now accept user-defined optimizers.

see changes to jobs/process/BaseSDTrainProcess.py which is needed in order for this to work. It simply edits a redundant lower() function so that user input case can be preserved for the dynamic import.

this will still allow using the same optimizers you had hard-coded so that it doesn't break current configs.

I have run several short tests with SDXL models to make sure it is training as expected and seems to work fully as expected.

Usage:
The user enters the full module and class name of the optimizer they want to use.
Examples:

• "prodigyplus.prodigy_plus_schedulefree.ProdigyPlusScheduleFree" (must be installed in the venv first - pip install prodigy-plus-schedule-free)
• "bitsandbytes.optim.PagedAdamW" - this is already installed with bitsandbytes. a great optimizer for getting around OOM errors. It uses paging to offload some of the load to the CPU without losing much if any training speed and no real quality loss. IMO it is faster than block swapping.
• "bitsandbytes.optim.PagedAdamW8bit"
• "bitsandbytes.optim.PagedLion"

Also would probably work just fine with other schedule free optimizers.