Fix .to_flat() to return df with ArrowDtype'd Series

[hombit]

Fixes #66

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.56%. Comparing base (a196bd6) to head (c081fef).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #73   +/-   ##
=======================================
  Coverage   97.56%   97.56%           
=======================================
  Files          16       16           
  Lines         820      821    +1     
=======================================
+ Hits          800      801    +1     
  Misses         20       20           

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[github-actions]

Before [a196bd6]	After [b7f041e]	Ratio	Benchmark (Parameter)
8.27±0.2ms	8.56±0.2ms	1.03	benchmarks.NestedFrameAddNested.time_run
257M	260M	1.01	benchmarks.AssignSingleDfToNestedSeries.peakmem_run
31.5±1ms	31.9±3ms	1.01	benchmarks.AssignSingleDfToNestedSeries.time_run
85.8M	86M	1	benchmarks.NestedFrameAddNested.peakmem_run
88.2M	88.2M	1	benchmarks.NestedFrameQuery.peakmem_run
88.2M	88.2M	1	benchmarks.NestedFrameReduce.peakmem_run
5.19±0.05ms	5.17±0.05ms	1	benchmarks.NestedFrameReduce.time_run
56.7±3ms	55.6±3ms	0.98	benchmarks.ReassignHalfOfNestedSeries.time_run
284M	272M	0.96	benchmarks.ReassignHalfOfNestedSeries.peakmem_run
8.95±0.05ms	6.14±0.03ms	0.69	benchmarks.NestedFrameQuery.time_run

Click here to view all benchmarks.

[dougbrn]

LGTM