refactor(client): upgrade socket2 to 0.6 and use version-specific API

crates/irtt-client/Cargo.toml

@@ -14,7 +14,7 @@ categories = ["network-programming"]
 [dependencies]
 irtt-proto.workspace = true
 libc = { version = "0.2", optional = true }
-socket2 = { version = "0.5", features = ["all"] }
+socket2 = { version = "0.6", features = ["all"] }
 thiserror = "2"
 
 [features]