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/router-macro/src/route_tree.rs

@@ -172,7 +172,7 @@ impl<'a> ParseRouteTree<'a> {
                         // If there is a dynamic segment, stop adding static segments
                         RouteSegment::Dynamic(..) => break,
                         RouteSegment::CatchAll(..) => {
-                            todo!("Catch all segments are not allowed in nests")
+                            unimplemented!("Catch all segments are not allowed in nests")
                         }
                     }
                 }