Optimize performance of NestedFrame.__getitem__ to get a single column

[smcguire-cmu]

Use the _is_nested_column method to improve single column performance.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.77%. Comparing base (cf288d7) to head (3191c91).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #379   +/-   ##
=======================================
  Coverage   97.77%   97.77%           
=======================================
  Files          19       19           
  Lines        2026     2026           
=======================================
  Hits         1981     1981           
  Misses         45       45           

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[github-actions]

Before [cf288d7] <v0.6.0>	After [6c0426a]	Ratio	Benchmark (Parameter)
31.9±0.5ms	33.0±0.6ms	1.03	benchmarks.AssignSingleDfToNestedSeries.time_run
176M	181M	1.03	benchmarks.ReadFewColumnsHTTPS.peakmem_run
244M	250M	1.02	benchmarks.AssignSingleDfToNestedSeries.peakmem_run
43.2±0.1ms	43.7±0.02ms	1.01	benchmarks.ReassignHalfOfNestedSeries.time_run
136M	136M	1	benchmarks.CountNestedBy.peakmem_run
102M	102M	1	benchmarks.NestedFrameAddNested.peakmem_run
107M	107M	1	benchmarks.NestedFrameQuery.peakmem_run
106M	106M	1	benchmarks.NestedFrameReduce.peakmem_run
2.06±0.02s	2.07±0.5s	1	benchmarks.ReadFewColumnsS3.time_run
64.4±0.7ms	63.7±0.5ms	0.99	benchmarks.CountNestedBy.time_run

Click here to view all benchmarks.

[dougbrn]

Thank you!