Re-export the axum feature flag under "server" (#2786)

* re-export the axum feature flag under "server"
* remove the axum prefix from all the fullstack examples

packages/fullstack/examples/streaming/src/main.rs

@@ -0,0 +1,41 @@
+use dioxus::prelude::*;
+use futures::StreamExt;
+use server_fn::codec::{StreamingText, TextStream};
+
+fn app() -> Element {
+    let mut response = use_signal(String::new);
+
+    rsx! {
+        button {
+            onclick: move |_| async move {
+                response.write().clear();
+                if let Ok(stream) = test_stream().await {
+                    response.write().push_str("Stream started\n");
+                    let mut stream = stream.into_inner();
+                    while let Some(Ok(text)) = stream.next().await {
+                        response.write().push_str(&text);
+                    }
+                }
+            },
+            "Start stream"
+        }
+        "{response}"
+    }
+}
+
+#[server(output = StreamingText)]
+pub async fn test_stream() -> Result<TextStream, ServerFnError> {
+    let (tx, rx) = futures::channel::mpsc::unbounded();
+    tokio::spawn(async move {
+        loop {
+            tokio::time::sleep(tokio::time::Duration::from_millis(500)).await;
+            let _ = tx.unbounded_send(Ok("Hello, world!".to_string()));
+        }
+    });
+
+    Ok(TextStream::new(rx))
+}
+
+fn main() {
+    launch(app)
+}