tests: overflow encountered in multiply

[pjonsson]

Here's an excerpt of the test logs:

2025-07-25 20:36:40 [info     ] Task commencing                task=AlchemistTask(dataset=Dataset <id=7e96b76a-6b02-4427-9a1d-3c9104f2db96 product=ga_ls7e_ard_3 location=s3://dea-public-data/baseline/ga_ls7e_ard_3/102/071/2020/09/09/ga_ls7e_ard_3-1-0_102071_2020-09-09_final.stac-item.json>, settings=AlchemistSettings(specification=Specification(measurements=['nbart_blue', 'nbart_green', 'nbart_red', 'nbart_nir', 'nbart_swir_1', 'nbart_swir_2', 'oa_fmask'], transform='wofs.virtualproduct.WOfSClassifier', transform_url='https://github.com/GeoscienceAustralia/wofs/', product=None, products=['ga_ls5t_ard_3', 'ga_ls7e_ard_3', 'ga_ls8c_ard_3'], measurement_renames={'oa_fmask': 'fmask'}, transform_args={'dsm_path': 'https://dea-public-data.s3-ap-southeast-2.amazonaws.com/projects/elevation/ga_srtm_dem1sv1_0/dem1sv1_0.tif'}, transform_args_per_product=None, resampling=None, override_product_family='ard', basis='nbart_green', aws_unsigned=True), output=OutputSettings(location='/tmp/alchemist', write_data_settings={'overview_resampling': <Resampling.mode: 6>}, nodata=1, preview_image=None, preview_image_singleband={'measurement': 'water', 'lookup_table': {0: [150, 150, 110], 1: [0, 0, 0], 16: [119, 104, 87], 32: [89, 88, 86], 64: [216, 215, 214], 80: [242, 220, 180], 128: [79, 129, 189], 160: [51, 82, 119], 192: [186, 211, 242]}}, metadata={'product_family': 'wo', 'producer': 'ga.gov.au', 'dataset_version': '1.6.0', 'collection_number': '3', 'naming_conventions': 'dea_c3'}, properties={'dea:dataset_maturity': 'interim'}, reference_source_dataset=True, write_stac=True, inherit_geometry=True, explorer_url='https://explorer.dev.dea.ga.gov.au/'), processing=ProcessingSettings(dask_chunks={'x': -1, 'y': 4096}, dask_client={})))
/usr/local/lib/python3.10/dist-packages/wofs/__init__.py:1: UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  from pkg_resources import get_distribution, DistributionNotFound
2025-07-25 20:36:45 [info     ] Data loaded                    task=UUID('7e96b76a-6b02-4427-9a1d-3c9104f2db96')
/usr/local/lib/python3.10/dist-packages/wofs/classifier.py:81: RuntimeWarning: divide by zero encountered in divide
  c = (a - b) / (a + b)
/usr/local/lib/python3.10/dist-packages/wofs/terrain.py:114: RuntimeWarning: overflow encountered in multiply
  norm_len = numpy.sqrt((xgrad * xgrad) + (ygrad * ygrad) + 1.0)

The overflow encountered in multiply doesn't sound like something that is done by design. It could be an issue with the test data, or wofs might need to do the intermediate multiplication with a larger datatype.