fix: CutoutInput improvements and upgrades

[HCookie]

Description

A couple improvements to the cutout input:

• Remove pre_processors from top level cutout
• Add _input to cutout states
• Alter CutoutInput to take a list to provide an explicit ordering

Closes #356

Additional notes

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📚 Documentation preview 📚: https://anemoi-inference--355.org.readthedocs.build/en/355/

[frazane]

Tested and solves the issue. Thanks!

[frazane]

Instead of an additional order key, why not consider #356?

[gmertes]

I agree with Francesco: can we do something more clever with the order? I like the idea of requiring the inputs to be specified as a list, this could be optional so we don't break backwards compatibility (or we make it a breaking change to avoid ambiguity).

[HCookie]

Sure, I'm happy to change it,
I think it will likely end up looking like

input:
  cutout:
		inputs:
	    - lam: ...
	    - global: ...