Fix as many test warnings as possible

[brendancol]

============ 468 passed, 320 warnings in 48.65s =============
xrspatial/tests/test_aspect.py: 1 warning
xrspatial/tests/test_classify.py: 2 warnings
xrspatial/tests/test_curvature.py: 1 warning
xrspatial/tests/test_focal.py: 9 warnings
xrspatial/tests/test_hillshade.py: 1 warning
xrspatial/tests/test_multispectral.py: 7 warnings
xrspatial/tests/test_slope.py: 1 warning
xrspatial/tests/test_viewshed.py: 4 warnings
/home/brendan/miniconda/envs/xrspatial-312/lib/python3.12/site-packages/numba_cuda/numba/cuda/dispatcher.py:696: NumbaPerformanceWarning: Grid size 1 will likely result in GPU under-utilization due to low occupancy.
warn(errors.NumbaPerformanceWarning(msg))

xrspatial/tests/test_classify.py::test_natural_breaks_not_enough_unique_values
/home/brendan/xarray-spatial/xrspatial/classify.py:612: Warning: natural_breaks Warning: Not enough unique values in data array for 18 classes. n_samples=17 should be >= n_clusters=18. Using k=17 instead.
warnings.warn('natural_breaks Warning: Not enough unique values '

xrspatial/tests/test_curvature.py: 264 warnings
/home/brendan/xarray-spatial/xrspatial/curvature.py:75: DeprecationWarning: Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future. Ensure you extract a single element from your array before performing this operation. (Deprecated NumPy 1.25.)
cellsize_arr = cupy.array([float(cellsize)], dtype='f4')

xrspatial/tests/test_focal.py::test_mean_transfer_function_gpu_equals_cpu
/home/brendan/miniconda/envs/xrspatial-312/lib/python3.12/site-packages/numba_cuda/numba/cuda/dispatcher.py:696: NumbaPerformanceWarning: Grid size 25 will likely result in GPU under-utilization due to low occupancy.
warn(errors.NumbaPerformanceWarning(msg))

xrspatial/tests/test_focal.py: 10 warnings
/home/brendan/miniconda/envs/xrspatial-312/lib/python3.12/site-packages/numba_cuda/numba/cuda/cudadrv/devicearray.py:934: NumbaPerformanceWarning: Host array used in CUDA kernel will incur copy overhead to/from device.
warn(NumbaPerformanceWarning(msg))

xrspatial/tests/test_focal.py::test_hotspots_zero_global_std
/home/brendan/xarray-spatial/xrspatial/focal.py:908: RuntimeWarning: invalid value encountered in divide
mean_array = convolve_2d(data, kernel / kernel.sum())

xrspatial/tests/test_hillshade.py::test_hillshade_rtx_with_shadows
/home/brendan/miniconda/envs/xrspatial-312/lib/python3.12/site-packages/numba_cuda/numba/cuda/dispatcher.py:696: NumbaPerformanceWarning: Grid size 16 will likely result in GPU under-utilization due to low occupancy.
warn(errors.NumbaPerformanceWarning(msg))

xrspatial/tests/test_pathfinding.py::test_a_star_search_with_barriers
xrspatial/tests/test_pathfinding.py::test_a_star_search_with_barriers
xrspatial/tests/test_pathfinding.py::test_a_star_search_with_barriers
xrspatial/tests/test_pathfinding.py::test_a_star_search_with_barriers
xrspatial/tests/test_pathfinding.py::test_a_star_search_with_barriers
xrspatial/tests/test_pathfinding.py::test_a_star_search_snap
xrspatial/tests/test_pathfinding.py::test_a_star_search_snap
/home/brendan/xarray-spatial/xrspatial/pathfinding.py:365: Warning: End at a non crossable location
warnings.warn("End at a non crossable location", Warning)

xrspatial/tests/test_pathfinding.py::test_a_star_search_snap
xrspatial/tests/test_pathfinding.py::test_a_star_search_snap
/home/brendan/xarray-spatial/xrspatial/pathfinding.py:357: Warning: Start at a non crossable location
warnings.warn("Start at a non crossable location", Warning)

xrspatial/tests/test_perlin.py::test_perlin_gpu
/home/brendan/miniconda/envs/xrspatial-312/lib/python3.12/site-packages/numba_cuda/numba/cuda/dispatcher.py:696: NumbaPerformanceWarning: Grid size 9 will likely result in GPU under-utilization due to low occupancy.
warn(errors.NumbaPerformanceWarning(msg))

xrspatial/tests/test_zonal.py::test_zone_ids_stats[dask+numpy]
xrspatial/tests/test_zonal.py::test_zone_ids_stats[dask+numpy]
/home/brendan/miniconda/envs/xrspatial-312/lib/python3.12/site-packages/dask/_task_spec.py:759: RuntimeWarning: invalid value encountered in divide
return self.func(*new_argspec)

xrspatial/tests/test_zonal.py::test_zone_ids_stats[dask+numpy]
xrspatial/tests/test_zonal.py::test_zone_ids_stats[dask+numpy]
/home/brendan/xarray-spatial/xrspatial/zonal.py:62: RuntimeWarning: All-NaN slice encountered
min=lambda block_mins: np.nanmin(block_mins, axis=0),

xrspatial/tests/test_zonal.py::test_zone_ids_stats[dask+numpy]
xrspatial/tests/test_zonal.py::test_zone_ids_stats[dask+numpy]
/home/brendan/xarray-spatial/xrspatial/zonal.py:61: RuntimeWarning: All-NaN slice encountered
max=lambda block_maxes: np.nanmax(block_maxes, axis=0),

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html