Inconsistent CRS state in Ribasim Python

[Hofer-Julian]

Even though we require crs during Model construction, we don't use it immediately.
It is only set when calling set_crs, which we do for example during saving:

Ribasim/python/ribasim/ribasim/model.py

Lines 163 to 164 in a5ee40f

	def _save(self, directory: DirectoryPath, input_dir: DirectoryPath):
	self.set_crs(self.crs)

We could pass crs to all member variables and use it already when adding nodes.