lastimport: Loved tracks from last.fm

sampsyo: "If we do this, one feature I'm interested in adding later is syncing of "loved" tracks—maybe even with a way to upload new :heart:s."
https://github.com/sampsyo/beets/issues/1007

I would really like that feature to be added. Currently I generate a playlist with all my loved tracks from musiccabinet, but it is not really practical. Maybe with that feature in beets, we could generate playlists based on a specific genre with only loved tracks?

Start by reviewing the existing lastimport command and the linked issue #1007 to understand current Last.fm support. Clarify whether the goal is importing loved tracks, uploading new loves, generating genre-specific playlists, or all three; define acceptance criteria before locating implementation and tests.

Written by the indexing model from the issue text.