Fix idx overflows in scatter_cuda kernel to enable benchmark/scatter_segment.py with long rows

[mikaylagawarecki]

This PR exists to show the "state of the world" for the "before" benchmark (rendered benchmarking results cuda)

• fixes CUDA illegal memory accesses run into by benchmarking script mentioned on #301 that are run into when src.numel() > std::numeric_limits<int>::max() on reduce options other than sum and mean
• Comments out arg kernel for max/min since we do not support argmax/argmin in core
• Some small edits to benchmark/scatter_segment.py

to reproduce errors on master prior to this PR run python benchmark/scatter_segment.py --reduce max, illegal memory accesses start occuring on the Janna dataset for size=128

[codecov-commenter]

Codecov Report

Merging #303 (4b34a87) into master (847995d) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #303   +/-   ##
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  Coverage   97.54%   97.54%           
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  Files           9        9           
  Lines         204      204           
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  Hits          199      199           
  Misses          5        5           

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[github-actions[bot]]

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