Extend Rust to Dart error propagation

[alexlapa]

Synopsis

Продолжаем #204 расширяя список прокидываемых через FFI ошибок.

Solution

1. Растовские HandlerDetached ошибки теперь прокидываются как дартовский стдшный StateError
2. Растовские MediaManagerError'ы теперь прокидываются как дартовский MediaManagerException.

Плюс небольшой рефакторинг футур Раст => Dart, а именно, обертка c тайп-параметром.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains Draft: prefix
  • [x] Name contains issue reference
  • [x] Has k:: labels applied
  • [x] Has assignee
• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
  • [x] Milestone is set
  • [x] PR's name and description are correct and up-to-date
  • [x] Draft: prefix is removed
  • [x] All temporary labels are removed

[alexlapa]

FCM

Extend Rust to Dart error propagation (#205)

- return weak pointer upgrade errors as Dart StateError
- return Jason's MediaManagerError as Dart MediaManagerException

Additionally:
- add convenience DartFuture wrapper for Futures returned from Rust to Dart
- fix peer::media::sender::State::new() return type