`interval_where_one` logic fails when using an (`xr.DataArray`, `float`) tuple

[aaTman]

When running tw_squared_error I ran into a bug that causes the code to fail out if the first object in the tuple for interval_where_one is an xr.DataArray and the second is a float, e.g. np.inf.

I think I pinpointed the issue:

scores/src/scores/continuous/threshold_weighted_impl.py

Lines 85 to 89 in 8117da8

	a, b = interval_where_one
	if isinstance(a, (float, int)):
	a = xr.DataArray(a)
	b = xr.DataArray(b)

Where b in this case will not be converted into a xr.DataArray, resulting in any methods, e.g. .min() failing.

I'll get a PR set up ASAP for y'all!

[aaTman]

Also, including tests here should address #813.