Accelerate item-item k-NN algorithms

[mdekstrand]

This significantly speeds up the item-item k-NN algorithm's scoring performance (by up to an order of magnitude).

It also removes the history lookup logic, so the k-NN scorer needs to be used with a history lookup component.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.57%. Comparing base (8418807) to head (6009cc9).
Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #578      +/-   ##
==========================================
- Coverage   90.68%   90.57%   -0.12%     
==========================================
  Files         107      108       +1     
  Lines        6624     6557      -67     
==========================================
- Hits         6007     5939      -68     
- Misses        617      618       +1     

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