PERF: DatetimeIndex constructor from list

[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/v1.6.0.rst file if fixing a bug or adding a new feature.

Improvement comes from avoiding np.ndim on a large list of objects.

ASVs added:

     [ac648eea]       [5e8af646]
     <main>           <perf-ensure-arraylike-for-datetimelike>
-      41.7±0.6ms         30.1±1ms     0.72  ctors.DatetimeIndexConstructor.time_from_list_of_str
-        239±20ms          110±1ms     0.46  ctors.DatetimeIndexConstructor.time_from_list_of_datetimes
-         243±3ms        111±0.6ms     0.46  ctors.DatetimeIndexConstructor.time_from_list_of_timestamps
-         242±5ms          108±1ms     0.45  ctors.DatetimeIndexConstructor.time_from_list_of_dates

[phofl]

A general note: I think our rule of thumb regarding benchmarks is: Around 20ms.

[lukemanley]

Sorry, I should have remembered. I just updated the asv to reduce the time:

       before           after         ratio
     [a712c501]       [a572dc1e]
     <main>           <perf-ensure-arraylike-for-datetimelike>
-     7.47±0.07ms      5.42±0.09ms     0.72  ctors.DatetimeIndexConstructor.time_from_list_of_str
-      44.0±0.4ms       20.5±0.4ms     0.47  ctors.DatetimeIndexConstructor.time_from_list_of_datetimes
-      43.6±0.2ms       19.9±0.2ms     0.46  ctors.DatetimeIndexConstructor.time_from_list_of_timestamps
-      42.9±0.6ms       19.4±0.2ms     0.45  ctors.DatetimeIndexConstructor.time_from_list_of_dates

[phofl]

Thx, no worries

[mroeschke]

LGTM. Merge when ready @phofl

[phofl]

thx @lukemanley