Incorporate implicit bridge into monorepo

[mdekstrand]

This advances the LensKit monorepo integration (#387) by integrating the implicit bridge.

[codecov]

Codecov Report

Attention: Patch coverage is 90.09901% with 10 lines in your changes missing coverage. Please review.

Project coverage is 90.93%. Comparing base (ebf66d6) to head (f92d4fe).
Report is 586 commits behind head on main.

Files with missing lines	Patch %	Lines
lenskit-implicit/lenskit/implicit.py	89.13%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #425      +/-   ##
==========================================
- Coverage   90.96%   90.93%   -0.04%     
==========================================
  Files          45       46       +1     
  Lines        3078     3176      +98     
==========================================
+ Hits         2800     2888      +88     
- Misses        278      288      +10     

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