Lyrics of the track's exact length can still be timed to another cut, and are never checked #716

The problem

Lyrics can run well ahead of the singer even when LRCLIB has a copy of exactly the track's length. Green Day's "Basket Case" video (https://www.youtube.com/watch?v=NUTGr5t3MoY) is 194 s, and so is the LRCLIB copy StemDeck keeps. That copy starts its first line at 0:00.05, while the video's singing starts around 0:16. At 0:33 the karaoke is already on "It all keeps adding up".

A version the track's length is taken as the track's own timing and never checked against the vocals. The check that moves lyrics onto the singing only runs for versions of another length. The same length proves nothing: a copy can be timed to another cut of the song.

Constraints for a fix

• Lyrics that are already right must never be nudged.
• A transcription and the file's own lyrics are the track's timing and stay as they are.
• A wrong move is worse than none, so a shift is applied only when the vocals show it clearly.

Found while testing the 0.18.2.dev0 build. Being worked on in the feat/song-identification branch.