Avoid whole-array computations required for Numba for now

[erogluorhan]

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There are a lot of places in the code where we convert Xarray data arrays to Numpy arrays (by calling .values) because they need to be used in a Numba-decorated function.

While this is understandable, this will need to be avoided for cases where the whole data array is bigger than or close to the available memory and hence is chunked, but such conversion of the whole data array into Numpy array would either break the execution or not run efficiently, respectively.

We will likely need to incorporate use of apply_ufunc-like mechanisms for such cases.