Fix singleton-range __setitem__ edge case

[wence-]

Description

When trying to set a length-one range with a length-one array, an off-by-one error in copying.copy_range meant that the value was discarded. Fix that, and tidy up the semantics of copy_range a little while we're here. Closes #12073.

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: 87.47% // Head: 88.11% // Increases project coverage by +0.63% 🎉

Coverage data is based on head (9e9c20a) compared to base (f817d96).
Patch has no changes to coverable lines.

Additional details and impacted files

@@               Coverage Diff                @@
##           branch-22.12   #12075      +/-   ##
================================================
+ Coverage         87.47%   88.11%   +0.63%     
================================================
  Files               133      135       +2     
  Lines             21826    22100     +274     
================================================
+ Hits              19093    19473     +380     
+ Misses             2733     2627     -106     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/interval.py	85.45% <0.00%> (-9.10%)	⬇️
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/cudf/cudf/io/json.py	92.06% <0.00%> (-2.68%)	⬇️
python/cudf/cudf/utils/utils.py	89.91% <0.00%> (-0.69%)	⬇️
python/cudf/cudf/core/column/timedelta.py	90.17% <0.00%> (-0.58%)	⬇️
python/cudf/cudf/core/column/datetime.py	89.21% <0.00%> (-0.51%)	⬇️
python/cudf/cudf/core/column/column.py	87.96% <0.00%> (-0.46%)	⬇️
python/dask_cudf/dask_cudf/core.py	73.72% <0.00%> (-0.41%)	⬇️
python/cudf/cudf/io/parquet.py	90.45% <0.00%> (-0.39%)	⬇️
... and 43 more

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[galipremsagar]

@gpucibot merge