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/01-app-demos/repo_readme.rs

@@ -0,0 +1,22 @@
+//! The example from the readme!
+//!
+//! This example demonstrates how to create a simple counter app with dioxus. The `Signal` type wraps inner values,
+//! making them `Copy`, allowing them to be freely used in closures and async functions. `Signal` also provides
+//! helper methods like AddAssign, SubAssign, toggle, etc, to make it easy to update the value without running
+//! into lock issues.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let mut count = use_signal(|| 0);
+
+    rsx! {
+        h1 { "High-Five counter: {count}" }
+        button { onclick: move |_| count += 1, "Up high!" }
+        button { onclick: move |_| count -= 1, "Down low!" }
+    }
+}