Packed data source builder
Add top-N MRR method
Make item selectors use TestUser
Add most-popular item selector
Fix bad cast in item selector
Delay javadoc runs until jars are built
Document metric thread safety
Use a metric to output user recommendations
Use a metric to output predictions.
Clean up unused recommend/predict layouts
Add missing license headers
Fix JavaDoc error
Clean up task ordering
Add type parameters to output metrics
Refactor live neighborhood finder

- Create NeighborFinder interface to replace NeighborhoodFinder
- Implement live and snapshot-based neighbor finders
Get the user-user tests running again
Measure the per-user test time.
Record per-user event counts
Bump vectorz dependency version
Improve FunkSVD cache locality

Use per-feature scratch vectors to improve the cache locality of building the FunkSVD recommender.