Is your feature request related to a problem? Please describe:

Right now, running a recipe on CPU (e.g. for debugging its initial setup) throws this error from "fairseq2/recipe/internal/device_stat.py":

fairseq2.recipe.error.DeviceTypeNotSupportedError: Only cpu and cuda devices are supported, but the device of the process is cpu.

Because no CPU DeviceStatTracker is registered here: "fairseq2/recipe/composition/device_stat.py".

Describe the solution you would like:

Possible solutions:

• Amend the error message to be consistent.
• Register the no-op tracker for the "cpu" type.
• Provide an actual default CPU stat tracker.

With a preference for the last one (which I think still lets recipe users override to implement their own CPU tracker).

Describe the alternatives you have considered:
As a simple bypass on the recipe implementer side, I simply registered the no-op stat tracker for the "cpu". Recipes are quite convenient!