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.

packages/playwright-tests/suspense-carousel/src/main.rs

@@ -111,7 +111,7 @@ fn NestedSuspendedComponent(id: i32) -> Element {
 fn main() {
     LaunchBuilder::new()
         .with_cfg(server_only! {
-            dioxus::fullstack::ServeConfig::builder().enable_out_of_order_streaming()
+            dioxus::server::ServeConfig::builder().enable_out_of_order_streaming()
         })
         .launch(app);
 }