Simplify set_crs and to_crs

[veenstrajelmer]

Current code in:

xugrid/xugrid/ugrid/ugridbase.py

Lines 596 to 627 in 699452b

	def set_crs(
	self,
	crs: Union["pyproj.CRS", str] = None, # type: ignore # noqa
	epsg: int = None,
	allow_override: bool = False,
	):
	"""
	Set the Coordinate Reference System (CRS) of a UGRID topology.
	NOTE: The underlying geometries are not transformed to this CRS. To
	transform the geometries to a new CRS, use the ``to_crs`` method.
	Parameters
	----------
	crs : pyproj.CRS, optional if `epsg` is specified
	The value can be anything accepted
	by :meth:`pyproj.CRS.from_user_input() <pyproj.crs.CRS.from_user_input>`,
	such as an authority string (eg "EPSG:4326") or a WKT string.
	epsg : int, optional if `crs` is specified
	EPSG code specifying the projection.
	allow_override : bool, default False
	If the the UGRID topology already has a CRS, allow to replace the
	existing CRS, even when both are not equal.
	"""
	import pyproj
	if crs is not None:
	crs = pyproj.CRS.from_user_input(crs)
	elif epsg is not None:
	crs = pyproj.CRS.from_epsg(epsg)
	else:
	raise ValueError("Must pass either crs or epsg.")

However, pyproj.CRS.from_user_input also correctly parses epsg integer values, so it is not necessary to do this separately.