Start using classes for Radio playlists and stations

[C0rn3j]

Radio playlists used multinested list of dictionaries, converted it to classes instead.

# From
radio_playlists: list[dict[str, int | str | list[dict[str, str]]]]
# To
radio_playlists: list[RadioPlaylist] 

• Exit if we fail to run migrations
• Requires a database bump (now 70)
• Corrects typing for RadioPlaylist variable in db_migrations
• Fixes gensokyoradio.net fallback URL (I thought I did that ages ago??)
• Stop setting scroll == 0 on Stations, it was there in one place in the code, makes no sense to me and seems like a mistake, should be set on Playlist instead?