codify "platform" into resolution logic, server-fn/fullstack overhaul (#4596)

overhaul dioxus fullstack using a new implementation of server_fn

This PR is a complete rewrite of dioxus fullstack designed to improve compatibility with axum and to fix a number of compilation errors based on feature flag unification plumbing through macros.

examples/05-using-async/suspense.rs

@@ -0,0 +1,62 @@
+//! Suspense in Dioxus
+//!
+//! Suspense allows components to bubble up loading states to parent components, simplifying data fetching.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app)
+}
+
+fn app() -> Element {
+    rsx! {
+        div {
+            h1 { "Dogs are very important" }
+            p {
+                "The dog or domestic dog (Canis familiaris[4][5] or Canis lupus familiaris[5])"
+                "is a domesticated descendant of the wolf which is characterized by an upturning tail."
+                "The dog derived from an ancient, extinct wolf,[6][7] and the modern grey wolf is the"
+                "dog's nearest living relative.[8] The dog was the first species to be domesticated,[9][8]"
+                "by hunter–gatherers over 15,000 years ago,[7] before the development of agriculture.[1]"
+            }
+            h3 { "Illustrious Dog Photo" }
+            ErrorBoundary { handle_error: |_| rsx! { p { "Error loading doggos" } },
+                SuspenseBoundary { fallback: move |_| rsx! { "Loading doggos..." },
+                    Doggo {}
+                }
+            }
+        }
+    }
+}
+
+#[component]
+fn Doggo() -> Element {
+    // `use_loader` returns a Result<Loader<T>, Loading>. Loading can either be "Pending" or "Failed".
+    // When we use the `?` operator, the pending/error state will be thrown to the nearest Suspense or Error boundary.
+    //
+    // During SSR, `use_loader` will serialize the contents of the fetch, and during hydration, the client will
+    // use the pre-fetched data instead of re-fetching to render.
+    let mut dog = use_loader(move || async move {
+        #[derive(serde::Deserialize, serde::Serialize, PartialEq)]
+        struct DogApi {
+            message: String,
+        }
+
+        reqwest::get("https://dog.ceo/api/breeds/image/random/")
+            .await
+            .unwrap()
+            .json::<DogApi>()
+            .await
+    })?;
+
+    rsx! {
+        button { onclick: move |_| dog.restart(), "Click to fetch another doggo" }
+        div {
+            img {
+                max_width: "500px",
+                max_height: "500px",
+                src: "{dog.read().message}"
+            }
+        }
+    }
+}