Testing and fixing NEMO spatialhash index_search

[erikvansebille]

This PR adds a unit test for spatial hash on 1/4 degree NEMO curvilinear grid (from https://github.com/OceanParcels/parcels-data/tree/main/data/NemoCurvilinear_data).

The unit test currently fails, because the spatial hash index returned is the cell on the anti-meridian (between 179.875 and 179.875; which technically also surrounds the location) instead of the cell that snugly surrounds the location

• Chose the correct base branch (main for v3 changes, v4-dev for v4 changes)
• Fixes Adding script for benchmarking the curvilinear search function parcels-benchmarks#5
• Added tests

[erikvansebille]

A simple change to the lines below seems to fix the failing unit test
https://github.com/OceanParcels/Parcels/blob/85f025be11cd122f8ac4bba463db2a97860c2549/parcels/spatialhash.py#L141-L150

- if xi1[eid] <= xi2[eid]:
+ if abs(xi1[eid] - xi2[eid]) > 225:
+     pass
+ elif xi1[eid] <= xi2[eid]:

This way, the grid cells that span the antemeridian (where the left corner is 179.875 and the right corner is -179.875) are not included in the hash table. However, we would need to make this work only when the field _mesh_type="spherical" (because on flat grids, it's to be expected that grid cells have distances of more than 225 meters between them)

@fluidnumerics-joe, does this give you some pointers/ideas how to fix the spatial hash.py function to make the unit test in this PR pass?

PS: Note that the 'special' value of 225 used above is also present in the v3-version of _index_search:
https://github.com/OceanParcels/Parcels/blob/fb88390d2bc9e2d45cd3056c601c7acaa9afcdac/parcels/_index_search.py#L253-L254

[erikvansebille]

Here's a map of the longitude grid

[erikvansebille]

With the new Morton having, this test passes. Good to pull it into the test-suite?