PERF: pd.concat with EA-backed indexes

[lukemanley]

• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/v2.0.0.rst file if fixing a bug or adding a new feature.

Perf improvement for pd.concat when objects contain EA-backed indexes. The bottleneck was EA.tolist. Still relatively slow vs non-EA, but an improvement.

$ asv continuous -f 1.1 upstream/main ea-tolist -b join_merge.ConcatIndexDtype before after ratio [90b4add7] [77a21f8d] <main> <ea-tolist> - 19.4±0.2ms 12.0±0.07ms 0.62 join_merge.ConcatIndexDtype.time_concat_series('Int64', 1, True, False) - 14.6±0.2ms 6.78±0.2ms 0.46 join_merge.ConcatIndexDtype.time_concat_series('Int64', 1, True, True) - 14.2±0.2ms 6.57±0.1ms 0.46 join_merge.ConcatIndexDtype.time_concat_series('Int64', 1, False, False) - 14.1±0.2ms 6.47±0.09ms 0.46 join_merge.ConcatIndexDtype.time_concat_series('Int64', 1, False, True) - 23.9±0.1ms 10.3±0.1ms 0.43 join_merge.ConcatIndexDtype.time_concat_series('string[python]', 1, True, False) - 19.7±0.3ms 5.53±0.05ms 0.28 join_merge.ConcatIndexDtype.time_concat_series('string[python]', 1, True, True) - 19.0±0.2ms 5.16±0.03ms 0.27 join_merge.ConcatIndexDtype.time_concat_series('string[python]', 1, False, True) - 18.5±0.2ms 4.82±0.03ms 0.26 join_merge.ConcatIndexDtype.time_concat_series('string[python]', 1, False, False) - 108±1ms 24.5±0.4ms 0.23 join_merge.ConcatIndexDtype.time_concat_series('string[pyarrow]', 1, True, False) - 98.4±0.6ms 17.0±0.3ms 0.17 join_merge.ConcatIndexDtype.time_concat_series('string[pyarrow]', 1, True, True) - 97.6±0.8ms 15.9±0.3ms 0.16 join_merge.ConcatIndexDtype.time_concat_series('string[pyarrow]', 1, False, True) - 99.2±0.5ms 16.0±0.3ms 0.16 join_merge.ConcatIndexDtype.time_concat_series('string[pyarrow]', 1, False, False) 

$ asv continuous -f 1.1 upstream/main ea-tolist -b array.ArrowStringArray before after ratio [90b4add7] [77a21f8d] <main> <ea-tolist> - 16.5±0.2ms 399±6μs 0.02 array.ArrowStringArray.time_tolist(True) - 17.1±0.2ms 404±6μs 0.02 array.ArrowStringArray.time_tolist(False) 

[jbrockmendel]

LGTM

[phofl]

thx @lukemanley