Integrate with `scores`

[Oisin-M]

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

HAT is xarray-based for hydrostats, so we could easily leverage scores, which is xarray-based also and already implements most (all?) of what we want.

Edit: one thing missing is 2012 version of KGE, but it has the 2009 version.

Describe the solution you'd like

More scores!

Describe alternatives you've considered

No response

Additional context

No response

Organisation

ECMWF