Allow BasicGrid serialization

[wpreimes]

For some reason Basic Grid can not be pkled, but CellGrid can. This can lead to issues with eg parallelization frameworks and should be fixed.

import cloudpickle
from pygeogrids.grids import CellGrid, BasicGrid

cloudpickle.dumps(CellGrid([1,2,3], [1,2,3], [1,2,3]))
print("Cellgrid could be pickled")
cloudpickle.dumps(BasicGrid([1,2,3], [1,2,3]))

Traceback (most recent call last):
  File "/home/wpreimes/miniforge3/envs/smecv_gapfill/lib/python3.10/site-packages/IPython/core/interactiveshell.py", line 3553, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-3-7762823bd9a7>", line 6, in <module>
    cloudpickle.dumps(BasicGrid([1,2,3], [1,2,3]))
  File "/home/wpreimes/miniforge3/envs/smecv_gapfill/lib/python3.10/site-packages/cloudpickle/cloudpickle.py", line 1479, in dumps
    cp.dump(obj)
  File "/home/wpreimes/miniforge3/envs/smecv_gapfill/lib/python3.10/site-packages/cloudpickle/cloudpickle.py", line 1245, in dump
    return super().dump(obj)
  File "<stringsource>", line 2, in pykdtree.kdtree.KDTree.__reduce_cython__
TypeError: no default __reduce__ due to non-trivial __cinit__
``