Implement ReduceNode for ScalarFnArray to avoid boxing

[robert3005]

fix #6436

[codspeed-hq]

Merging this PR will not alter performance

✅ 1135 untouched benchmarks
⏩ 1268 skipped benchmarks¹

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_{Comparing rk/reducenode (47d5477) with develop (39425ae)²}

Footnotes

1. 1268 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on develop (dbe0ff5) during the generation of this report, so 39425ae was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩

[joseph-isaacs]

do we need this?

[joseph-isaacs]

There is a horrible naming in the trait