List lengths property for extension array and accessor

[hombit]

I believe it is very useful to have, the alternative is calling something like

ndf[nested].nest.to_lists()["some_column_name"].list.len()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.43%. Comparing base (61ed4f1) to head (63f5524).
Report is 182 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #198      +/-   ##
==========================================
+ Coverage   98.41%   98.43%   +0.01%     
==========================================
  Files          13       13              
  Lines        1138     1152      +14     
==========================================
+ Hits         1120     1134      +14     
  Misses         18       18              

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[github-actions]

Before [d09e044]	After [ab370ca]	Ratio	Benchmark (Parameter)
39.6±8ms	41.2±8ms	1.04	benchmarks.ReassignHalfOfNestedSeries.time_run
25.9±0.8ms	26.1±0.3ms	1.01	benchmarks.AssignSingleDfToNestedSeries.time_run
1.23±0.01ms	1.24±0ms	1.01	benchmarks.NestedFrameReduce.time_run
269M	270M	1	benchmarks.AssignSingleDfToNestedSeries.peakmem_run
92M	92M	1	benchmarks.NestedFrameAddNested.peakmem_run
96.4M	96.4M	1	benchmarks.NestedFrameQuery.peakmem_run
95.6M	95.6M	1	benchmarks.NestedFrameReduce.peakmem_run
288M	289M	1	benchmarks.ReassignHalfOfNestedSeries.peakmem_run
10.3±0.2ms	10.0±0.1ms	0.98	benchmarks.NestedFrameAddNested.time_run
10.9±0.05ms	10.7±0.05ms	0.98	benchmarks.NestedFrameQuery.time_run

Click here to view all benchmarks.

[gitosaurus]

LGTM!