Share Rust log messages with Dart

[holzeis]

Send Rust logs to Flutter via stream so that they can be included in the file output (and have unified logging).

see: https://cjycode.com/flutter_rust_bridge/feature/logging.html

[klochowicz]

@holzeis I edited the ticket name and description to better convey what we still need to do here. I will proceed with this, as having a working tracing infrastructure will make the LN integration much easier.