ENH: Make _to_dataframe faster for extension array columns after pandas fix

[ilan-gold]

What is your issue?

One pandas-dev/pandas#57676 is completed, we should be able to do the joins in the _to_dataframe method faster (we need to be able to handle the singleton case which is hte issue with pandas):

xarray/xarray/core/dataset.py

Lines 7170 to 7177 in 239309f

	def _to_dataframe(self, ordered_dims: Mapping[Any, int]):
	columns = [k for k in self.variables if k not in self.dims]
	data = [
	self._variables[k].set_dims(ordered_dims).values.reshape(-1)
	for k in columns
	]
	index = self.coords.to_index([*ordered_dims])
	return pd.DataFrame(dict(zip(columns, data)), index=index)

see discussion here