fix: flutter_rust_bridge version compatibility

[ethicnology]

Hey there,

I would like to ask if there is any reason to restrict flutter_rust_bridge between >=2.0.0 and <2.1.0 instead of ^2.0.0 or ^2.1.0 ?

This create incompatibility with packages that rely on more updated versions of flutter_rust_bridge, currently ^2.6.0

Example:

flutter pub add bip85

Because every version of bip85 depends on flutter_rust_bridge ^2.6.0 and every version of lwk_dart
  from git depends on flutter_rust_bridge 2.0.0, bip85 is incompatible with lwk_dart from git.
So, because bb_mobile depends on both lwk_dart from git and bip85 any, version solving failed.