Cython API refactor: merge.pyx

[isVoid]

This PR refactors merge_sorted in merge.pyx to accept a list of columns, contributes to #10153

[codecov]

Codecov Report

Merging #10698 (d8a61fc) into branch-22.06 (65b1cbd) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@               Coverage Diff                @@
##           branch-22.06   #10698      +/-   ##
================================================
+ Coverage         86.35%   86.39%   +0.04%     
================================================
  Files               142      142              
  Lines             22335    22302      -33     
================================================
- Hits              19287    19268      -19     
+ Misses             3048     3034      -14     

Impacted Files	Coverage Δ
python/cudf/cudf/core/reshape.py	90.00% <100.00%> (+0.17%)	⬆️
python/cudf/cudf/core/column/column.py	89.43% <0.00%> (-0.02%)	⬇️
python/cudf/cudf/core/frame.py	93.41% <0.00%> (ø)
python/cudf/cudf/core/series.py	95.15% <0.00%> (ø)
python/cudf/cudf/core/dataframe.py	93.75% <0.00%> (+<0.01%)	⬆️
python/cudf/cudf/utils/utils.py	90.35% <0.00%> (+0.06%)	⬆️
python/cudf/cudf/core/column/string.py	89.21% <0.00%> (+0.10%)	⬆️
python/cudf/cudf/testing/_utils.py	93.98% <0.00%> (+0.13%)	⬆️
python/cudf/cudf/core/multiindex.py	92.28% <0.00%> (+0.13%)	⬆️
python/cudf/cudf/core/column/categorical.py	89.97% <0.00%> (+0.20%)	⬆️
... and 4 more

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[shwina]

Minor nit

[isVoid]

rerun tests

[isVoid]

@gpucibot merge