Avoid copy in count / logical nulls

[alamb]

This is a proposed improvement of apache#8511 to avoid copying Null Buffers in the count aggregator.

Note this targets apache#8511

I will also file a proposal to upstream this change into arrow-rs

cc @joroKr21 and @Dandandan

[joroKr21]

Ok I see - it kinda makes sense, you handle the known types in a pattern match.
It's unlikely new types will be added before we can upstream this change 👍

[alamb]

I think this may be overkill -- apache#8511 (review)

Closing this PR and let's keep the code simple unless we find some profile or benchmark where it matters

[alamb]

Doh, just missed it !