Primod's basin mapping can't deal with integer basin id's with latest Rasterio dependecy

[HendrikKok]

problem: imod.prepare.rasterize results in a crash if node_id is an integer and fill-value is the default np.nan.

solution: We could use a fill-value of 0 if node_id is integer but this does not work in combination with NodeBasinMapping logic. Best is to force node_id to float64 dtype.

[JoerivanEngelen]

FYI: This is an issue with rasterio >=1.3.10.

Setting fillid to -1 caused the tests to succeed, but I don't know if this aspect is well tested.

Update: This is not true; test_ribamod_partial_two_basin fails, which indicates my solution doesn't work immediately

[JoerivanEngelen]

FYI, as it is related: In this PR #348 I had to force the dtype argument for imod.prepare.rasterize to float, otherwise problems arose.

I recently updated iMOD Python to take a dtype argument for its rasterize function, but haven't released this yet. The branch uses a dev install of iMOD Python now.