Put LightGCN in eval mode after training (2025)

[mdekstrand]

This adds a model.eval() call to the LightGCN trainer's finalize(), to put the model in eval mode before inference.

This is the 2025.x version of the change.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.95%. Comparing base (73066ec) to head (771c508).
⚠️ Report is 1 commits behind head on series/2025.

Additional details and impacted files

@@             Coverage Diff              @@
##           series/2025     #975   +/-   ##
============================================
  Coverage        88.95%   88.95%           
============================================
  Files              215      215           
  Lines            14961    14961           
============================================
  Hits             13308    13308           
  Misses            1653     1653           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.