refactor: replace std::sync::mpsc with flume for improved channel performance

Migrate internal message passing to flume to leverage better performance and additional features like eventual fairness and selection.

Cargo.toml

@@ -28,6 +28,7 @@ rustix = { version = "1.1", features = ["fs", "system", "thread", "time"] }
 rust-uci = { git = "https://github.com/namib-project/rust-uci.git", rev = "71ea7864ae5d266100043bfd2f682d4302a5b3fc", optional = true }
 thiserror = "2.0"
 libc = "0.2"
+flume = { version = "0.12.0",  default-features = false, features = ["eventual-fairness", "select"] }
 
 [dependencies.log]
 features = ["std"]