rename "Lenskit" to LensKit for consistency

[mdekstrand]

This is a small internal tweak to rename a few classes called LenskitXX to LensKitXX for consistency with branding.

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 89.98%. Comparing base (f24d461) to head (f5a0422).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
lenskit/lenskit/parallel/pool.py	80.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #602   +/-   ##
=======================================
  Coverage   89.98%   89.98%           
=======================================
  Files         107      107           
  Lines        6608     6608           
=======================================
  Hits         5946     5946           
  Misses        662      662           

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