Use pragma once

[bdice]

Description

This PR adapts a few files using header guards with #ifndef… #define to use #pragma once instead. This establishes a more consistent code style for the library.

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: 88.13% // Increases project coverage by +0.72% 🎉

Coverage data is based on head (cd6c187) compared to base (f72c4ce).
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #12019      +/-   ##
================================================
+ Coverage         87.40%   88.13%   +0.72%     
================================================
  Files               133      133              
  Lines             21833    21982     +149     
================================================
+ Hits              19084    19373     +289     
+ Misses             2749     2609     -140     

Impacted Files	Coverage Δ
python/strings_udf/strings_udf/__init__.py	86.27% <0.00%> (-10.61%)	⬇️
python/cudf/cudf/io/text.py	91.66% <0.00%> (-8.34%)	⬇️
python/cudf/cudf/core/_base_index.py	81.28% <0.00%> (-4.27%)	⬇️
python/strings_udf/strings_udf/_typing.py	94.73% <0.00%> (-1.06%)	⬇️
python/cudf/cudf/utils/utils.py	89.91% <0.00%> (-0.69%)	⬇️
python/cudf/cudf/testing/dataset_generator.py	72.83% <0.00%> (-0.42%)	⬇️
python/dask_cudf/dask_cudf/core.py	73.72% <0.00%> (-0.41%)	⬇️
python/dask_cudf/dask_cudf/backends.py	84.90% <0.00%> (-0.37%)	⬇️
python/cudf/cudf/core/dataframe.py	93.67% <0.00%> (-0.10%)	⬇️
python/cudf/cudf/io/orc.py	92.94% <0.00%> (-0.09%)	⬇️
... and 24 more

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[bdice]

@gpucibot merge