Fix nested rsx expansion by not using template titles (#2799)

* Fix nested rsx expansion by not using template titles

* fix writers with nameless templates

* fix clippy

* dont commit vscode fix

* fix release mode, pull out __template_name

* fix axum_desktop

* Fix core tests

* Make most fields of HotReloadedTemplate public for testing

* wip: formatting, compare all diff cases

* slightly smarter diffing for dynamic nodes

* add a comment about generic node diffing

* clean up mutations a bit

* fix load template

* simplify maybe_rebuild

* Restore write mutations flag in web

* write_mutations -> skip_mutations

---------

Co-authored-by: Evan Almloff <evanalmloff@gmail.com>

packages/core/src/arena.rs

@@ -27,10 +27,10 @@ impl MountId {
     pub(crate) const PLACEHOLDER: Self = Self(usize::MAX);
 
     pub(crate) fn as_usize(self) -> Option<usize> {
-        if self == Self::PLACEHOLDER {
-            None
-        } else {
+        if self.mounted() {
             Some(self.0)
+        } else {
+            None
         }
     }