[ENH]: Use null-safe dependencies

Is your feature request related to a problem? Please describe. Both flutter_sound and flutter_sound_lite depend on older dependencies, thus projects that depend on fluter_sound or flutter_sound_light cannot be upgraded to null-safe code.

Describe the solution you’d like Upgrade dependencies, e.g.:

dependencies:
  flutter_spinkit: ^5.0.0
  logger: ^1.0.0-nullsafety.0
  path: ^1.8.0
  path_provider: ^2.0.1
  provider: ^5.0.0
  recase: ^3.0.1
  synchronized: ^3.0.0
  uuid: ^3.0.1

Describe alternatives you’ve considered sorry, none

Additional context Note that you can mix null-safe and other code now, compare https://dart.dev/null-safety/migration-guide

[Larpoux]

@robert-virkus :

Finally, I decided to work on this issue, now. You can expect to get a new branch which will be null-safety compliant some time next week.

[robert-virkus]

Wow, that was quick! Thanks, for me everything works fine!!!