feat(client): add optional Tokio socket support

crates/irtt-client/Cargo.toml

@@ -16,10 +16,17 @@ irtt-proto.workspace = true
 libc = { version = "0.2.189", optional = true }
 socket2 = { version = "0.6.5", features = ["all"] }
 thiserror = "2.0.19"
+tokio = {
+    version = "1",
+    default-features = false,
+    features = ["rt", "net", "time", "sync"],
+    optional = true,
+}
 
 [features]
 default = []
 ancillary = ["dep:libc"]
+tokio = ["dep:tokio"]
 
 [package.metadata.docs.rs]
 all-features = true