feat(wireguard-broker): merge from dev/broker-architecture, fixes, test

* wireguard-broker: merge from dev/broker-architecture
* use zerocopy instead of lenses
* Require use_broker feature flag to comile broker binaries
* Remove PhantomData from BrokerServer & BrokerClient
* Modify mio client rx to be non-recursive, add integration test

Co-authored-by: Karolin Varner <karo@cupdev.net>
Co-authored-by: Prabhpreet Dua <615318+prabhpreet@users.noreply.github.com>

wireguard-broker/src/api/mod.rs

@@ -0,0 +1,4 @@
+pub mod client;
+pub mod mio_client;
+pub mod msgs;
+pub mod server;