Fix decimal benchmark input data generation

[karthikeyann]

Description

closes #11850
Fixes decimal benchmark input data generation.
Generated data alternated between two values because device_uvector<T> has both value and scale. scale is fixed for a column and hence when this data is copied to cudf::column, this column values alternated between values and scale.
Fix is to use device_storage_type_t<T> instead of T.

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[codecov]

Codecov Report

Base: 87.40% // Head: 87.49% // Increases project coverage by +0.08% 🎉

Coverage data is based on head (99ff519) compared to base (f72c4ce).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #11863      +/-   ##
================================================
+ Coverage         87.40%   87.49%   +0.08%     
================================================
  Files               133      133              
  Lines             21833    21830       -3     
================================================
+ Hits              19084    19101      +17     
+ Misses             2749     2729      -20     

Impacted Files	Coverage Δ
python/cudf/cudf/core/udf/__init__.py	50.00% <ø> (ø)
python/cudf/cudf/utils/ioutils.py	79.47% <ø> (ø)
...thon/dask_cudf/dask_cudf/tests/test_distributed.py	18.86% <ø> (+4.94%)	⬆️
python/cudf/cudf/__init__.py	90.69% <100.00%> (ø)
python/cudf/cudf/core/scalar.py	90.52% <100.00%> (+1.25%)	⬆️
python/dask_cudf/dask_cudf/sorting.py	93.29% <100.00%> (+2.11%)	⬆️
python/strings_udf/strings_udf/__init__.py	86.27% <100.00%> (-10.61%)	⬇️
python/strings_udf/strings_udf/_typing.py	94.73% <0.00%> (-1.06%)	⬇️
python/cudf/cudf/testing/dataset_generator.py	72.83% <0.00%> (-0.42%)	⬇️
... and 2 more

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[karthikeyann]

@gpucibot merge