Add byte conversion to allow int NBT values for Fireworks

[rtm516]

Fixes #679

[Arktisfox]

Would Integer.valueOf( nbt tag ).byteValue(); work better here, instead of converting to string and back?

[rtm516]

Would Integer.valueOf( nbt tag ).byteValue(); work better here, instead of converting to string and back?

No because it is sometimes a byte and sometimes an int, whereas that only takes int or string, so it would need a toString again

[Arktisfox]

Tested on Paper with the commands listed in the issue, appears to be fixed (both entity and item forms)