Remove redundant generic argument from Aggregator

[fraillt]

Basically remove reduntant code (it was introduced in initial revision, but during review process interface changes, so it left here by accident), and simplify Aggregator trait.

Changes

Please provide a brief description of the changes here.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.4%. Comparing base (fcd7cae) to head (d89e4f9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #2269   +/-   ##
=====================================
  Coverage   79.4%   79.4%           
=====================================
  Files        121     121           
  Lines      20981   20981           
=====================================
  Hits       16673   16673           
  Misses      4308    4308           

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