Some complex aggregations broken with `numbagg` installed

What happened?

Some common aggregations (at least min, max, var, std) are broken with complex dtypes if numbagg is installed with the default skipna=True. Looks like this is the case since #8624.

What did you expect to happen?

We either route to bottleneck or numpy here if these aggregation aren't supported in numbagg, or get them working with numbagg.

Minimal Complete Verifiable Example

import xarray as xr
import numpy as np
da = xr.DataArray(np.ones((2,), dtype=np.complex_), dims=["x"])
da.min(skipna=False) # works
da.min() # fails

MVCE confirmation

[X] Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
[X] Complete example — the example is self-contained, including all data and the text of any traceback.
[X] Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
[X] New issue — a search of GitHub Issues suggests this is not a duplicate.
[X] Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

TypeError: ufunc '__numbagg_transformed_func' not supported for the input types, and the inputs could not be safely coerced to any supported types according to the casting rule ''safe''

Anything else we need to know?

cc @max-sixty

Environment

xarray==2024.1.1 numbagg==0.8.1

pydata / xarray

Some complex aggregations broken with `numbagg` installed #9209