Improved performance of max(), min(), argMin(), argMax() for DateTime64

[Enmk]

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Changelog category (leave one):

• Performance Improvement

Changelog entry (up to few sentences, required except for Non-significant/Documentation categories):
Improved performance of max(), min(), argMin(), argMax() for DateTime64
...

Detailed description (optional):
This boost performance of min/max on my machine by factor of 2:
pre-fix query performance on hits_v1 dataset with perftest:

Query	Execution time (seconds)
SELECT max(x) FROM dt	[0.006]
SELECT max(x) FROM dt64	[0.046]

max on DateTime64 is 0.046 / 0.006 = 7.666666666666666 slower (A)

post-fix performance:

Query	Execution time (seconds)
SELECT max(x) FROM dt	[0.005]
SELECT max(x) FROM dt64	[0.018]

max on DateTime64 is 0.018 / 0.005 = 3.5999999999999996 slower (B)

Gain is:
(A - B) / A * 100 % = 53%

[alexey-milovidov]

Is this code identical to what we already have in master?

[Enmk]

Is this code identical to what we already have in master?

almost, I haven't noticed that something like that was already done. However, there are missing specializations in master:

if (which.idx == TypeIndex::DateTime64)
   // ...

Let me fixup the PR to include only that.

[Enmk]

Let me fixup the PR to include only that.

Done