Songs with tempo changes but no tempo variation have tempo displayed as a range #39

If a song has a tempo changer, its tempo will be displayed in the song's page in the form of a range ([start]–[end] t/s ([start]–[end] BPM)). A tempo changer being present determines how the tempo will be stored in the song document (either as tempo, a single value, or as tempoRange, a pair of values).

But if there's only a single tempo changer, or multiple tempo changers set to the same value — such that the end result effectively acts like there are no tempo changers —, a range will be displayed with the same start and end value. An example can be seen here: https://noteblock.world/song/b5TvI1wXc7

The problem can be fixed easily in the frontend by detecting if the start and end of the range are the same, and, if so, only displaying a single value.
(It's still useful to have songs with tempo changers have that information stored internally; though at some point it would be wise to review if that's the best representation.)