fix(spotify): map Pathfinder track metadata

[theDimZone]

I wanted to use spogo for my tool and have noticed that it doesn't show duration in json output. Fixed it with heavy codex assistance.

Summary

This fixes missing track metadata when playlist, library, and track info results come from Spotify's Pathfinder payloads.

Pathfinder does not always expose track duration as top-level duration_ms or durationMs. Depending on the endpoint, it can be nested under duration.totalMilliseconds or trackDuration.totalMilliseconds.

A few other track fields also use Pathfinder-specific shapes:

• explicit metadata comes from contentRating.label
• playability comes from playability.playable

This PR adds support for those shapes, and keeps explicit: false visible in JSON when we know the value is actually present.