avoid setting `force_ndarray_like = True`

Moving to a separate issue to be able to properly track this.

Why does pint-xarray require pint.application_registry.force_ndarray_like = True in the first place? I don't like when my dependencies force me to force something... This has become an issue because that very same setting is incompatible with pint-pandas: https://github.com/hgrecco/pint-pandas/issues/165. Given that xarray bases on pandas, this seems to be somewhat serious.

Originally posted by @burnpanck in https://github.com/xarray-contrib/pint-xarray/issues/189#issuecomment-1532145519

The reason is that xarray detects a duck array using a certain interface, casting everything that does not satisfy that to numpy using np.asarray. Since python scalars (float, int) don't have the ndim, dtype and shape properties (though pint does default ndim to 0), the result of some numpy functions will be cast, dropping the units.

Requiring force_ndarray_like avoids that, since pint will do the casting before xarray can do it. I agree that this feels like a hack, though.

Originally posted by @keewis in https://github.com/xarray-contrib/pint-xarray/issues/189#issuecomment-1542549750

Hm. I have a feeling that this is again a reason for implementing separate pint.QuantityArray and pint.QuantityScalar types - because IMHO pint should never respond to np.asarray by stripping units.

Either way, pint-pandas does not require it, and managed to get most operations to work without stripping units. There, it is up to the user to make sure that their objects make it into pandas as a PintArray, e.g. by setting force_ndarray_like = True, or simply by directly building a PintArray. But once the quantity arrays are in, pandas operations do not strip units (at least things improved significantly). Given that, in most cases, users of both xarray and pandas work with arrays anyways, it feels like forcing force_ndarray_like = True on every user is rather harsh. Even more so by doing it at import time - causing an import order dependency!

Originally posted by @burnpanck in https://github.com/xarray-contrib/pint-xarray/issues/189#issuecomment-1542765093

Start by reviewing the issue discussion, the xarray duck-array integration documentation, and the linked pint-pandas issue. Investigate where pint.application_registry.force_ndarray_like is required and how it is set at import time. Done should mean the dependency no longer forces this setting while preserving units and compatibility with both xarray and pint-pandas.