Split FunkSVD into separate package in a monorepo

[mdekstrand]

This addresses #378 by moving FunkSVD into a separate package, also laying the groundwork for #387. Closes #378.

[codecov]

Codecov Report

Attention: Patch coverage is 62.96296% with 10 lines in your changes missing coverage. Please review.

Project coverage is 91.34%. Comparing base (2d39bd6) to head (2b184cb).
Report is 683 commits behind head on main.

Files with missing lines	Patch %	Lines
lenskit/lenskit/datasets/fetch.py	0.00%	7 Missing ⚠️
lenskit/lenskit/parallel/config.py	72.72%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #418      +/-   ##
==========================================
+ Coverage   90.47%   91.34%   +0.87%     
==========================================
  Files          48       48              
  Lines        3201     3200       -1     
==========================================
+ Hits         2896     2923      +27     
+ Misses        305      277      -28     

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