Improve performance of the SUM accumulator

[alamb]

Is your feature request related to a problem or challenge?

While working on #6800 / #4973 I noticed that the SUM accumulators intermediate state contains two fields:

• sum: Native
• count: usize

Maintaining this state is on the hit path of the aggregates (e.g. TPCH Q1 has 4 of sums) thus reducing the work is performance critical

The counts are only needed for the retractable version of the accumulator (aka sliding accumulator used in window functions) but they are actually carried through all implementations.

Sum accumulator is here https://github.com/apache/arrow-datafusion/blob/main/datafusion/physical-expr/src/aggregate/sum.rs

Describe the solution you'd like

I would like to remove the counts field in the sum accumulator (or only use it when we have sliding windows)

Describe alternatives you've considered

No response

Additional context

No response