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/04-managing-state/memo_chain.rs

@@ -0,0 +1,45 @@
+//! This example shows how you can chain memos together to create a tree of memoized values.
+//!
+//! Memos will also pause when their parent component pauses, so if you have a memo that depends on a signal, and the
+//! signal pauses, the memo will pause too.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let mut value = use_signal(|| 0);
+    let mut depth = use_signal(|| 0_usize);
+    let items = use_memo(move || (0..depth()).map(|f| f as _).collect::<Vec<isize>>());
+    let state = use_memo(move || value() + 1);
+
+    println!("rendering app");
+
+    rsx! {
+        button { onclick: move |_| value += 1, "Increment" }
+        button { onclick: move |_| depth += 1, "Add depth" }
+        button { onclick: move |_| depth -= 1, "Remove depth" }
+        if depth() > 0 {
+            Child { depth, items, state }
+        }
+    }
+}
+
+#[component]
+fn Child(state: Memo<isize>, items: Memo<Vec<isize>>, depth: ReadSignal<usize>) -> Element {
+    // These memos don't get re-computed when early returns happen
+    let state = use_memo(move || state() + 1);
+    let item = use_memo(move || items()[depth() - 1]);
+    let depth = use_memo(move || depth() - 1);
+
+    println!("rendering child: {}", depth());
+
+    rsx! {
+        h3 { "Depth({depth})-Item({item}): {state}"}
+        if depth() > 0 {
+            Child { depth, state, items }
+        }
+    }
+}