issue in mesh2mesh_swarm due to recent pykdtree switch

[gthyagi]

@lmoresi

Could you please look into this error?

File "/Users/tgol0006/manual_install_pkg/petsc_venv_uw3_21125/venv_uw3/lib/python3.11/site-packages/underworld3/adaptivity.py", line 403, in mesh2mesh_meshVariable
    tmp_swarm1 = mesh2mesh_swarm(
                 ^^^^^^^^^^^^^^^^
  File "/Users/tgol0006/manual_install_pkg/petsc_venv_uw3_21125/venv_uw3/lib/python3.11/site-packages/underworld3/adaptivity.py", line 271, in mesh2mesh_swarm
    found1 = np.where(cell >= 0)[0]
             ^^^^^^^^^^^^^^^^^^^
ValueError: Calling nonzero on 0d arrays is not allowed. Use np.atleast_1d(scalar).nonzero() instead. If the context of this error is of the form `arr[nonzero(cond)]`, just use `arr[cond]`.

I am using dev branch.

box_3d_refined_iso_visc.py.txt

box_3d_refined_around_fault.msh.zip

fault_surface.msh.zip