perf : Optimize count distinct

[coderfender]

Which issue does this PR close?

Remove hashset based accumulators for smaller int data types and use bitmaps. Follow up of : #21453

• Closes #.

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[coderfender]

benchmark results :

count_distinct i16 bitmap                      1.00      3.3±0.43µs        ? ?/sec    23.87    78.4±0.84µs        ? ?/sec
count_distinct i8 bitmap                       1.00      2.3±0.49µs        ? ?/sec    7.13     16.7±0.55µs        ? ?/sec
count_distinct u16 bitmap                      1.00      3.1±0.18µs        ? ?/sec    25.45    78.8±3.92µs        ? ?/sec
count_distinct u8 bitmap                       1.00      2.3±0.34µs        ? ?/sec    7.37     16.9±0.14µs        ? ?/sec

It seems like we are 25x faster for u16 bitmap based accumulators (or I am sleepy :) )

[Dandandan]

I think we can do the same for 16 bit types, it is just 65_536 bytes 8192 if we use a bitmap.

[Dandandan]

Oh wait, you're already doing that :)