Xelis 1.19 Compatibility

[Tritonn204]

This PR migrates the Xelis integration in Stack to use the new FFI bindings for 1.19, which involved some straightforward (but still breaking) API changes and dep updates. This draft has been created to make the team aware of this pivot, while I re-sync to staging instead of main.

TODO:

• Synchronize to staging
• Walk back as many dep/build changes as possible (staging sync eliminated the need)
• ID any points of confusion in the devops AFTER syncing to staging
• Sync my xelis-dart-sdk work to Slixe's parallel updates to fix current Genesix
• Re-solidify the Xelis FFI dep tree to use the real endpoints instead of my forks
• Make PR for downstream cypherstack/xelis-flutter-ffi w/ new API
• Document the noteworthy mentionables for the team on this thread to allow asynchronous sync-ups

[Tritonn204]

Dart >= 3.1.0 is required, but docs pin the Flutter version to 3.35.7 which ships with only Dart 3.9.2.