minor: Add microbenchmark for integer sum with grouping

[andygrove]

Which issue does this PR close?

N/A

Rationale for this change

I am using this to test the changes in #2600

What changes are included in this PR?

How are these changes tested?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.31%. Comparing base (f09f8af) to head (0ca860e).
⚠️ Report is 715 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2805      +/-   ##
============================================
+ Coverage     56.12%   58.31%   +2.18%     
- Complexity      976     1422     +446     
============================================
  Files           119      162      +43     
  Lines         11743    14145    +2402     
  Branches       2251     2363     +112     
============================================
+ Hits           6591     8248    +1657     
- Misses         4012     4704     +692     
- Partials       1140     1193      +53     

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[coderfender]

Thank you @andygrove

[comphead]

Thanks @andygrove