Fix render-expr in eval position: wrap result in raw-html

The spec's eval-list calls render-expr for HTML tags/components in eval
position but returned a plain string. When that string was later passed
through _arender (e.g. as a component keyword arg), it got HTML-escaped.

Fix in eval.sx: wrap render-expr result in make-raw-html so the value
carries the raw-html type through any evaluator boundary. Also add
is_render_expr check in async_eval_ref.py as belt-and-suspenders for
the same issue in the async wrapper.

This fixes the streaming demo where suspense placeholder divs were
displayed as escaped text instead of real DOM elements.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/ref/eval.sx

@@ -172,9 +172,12 @@
                 (let ((mac (env-get env name)))
                   (make-thunk (expand-macro mac args env) env))
 
-              ;; Render expression — delegate to active adapter
+              ;; Render expression — delegate to active adapter.
+              ;; Wrap in raw-html so the result keeps its type when
+              ;; used as a value in eval position (e.g. bound to a
+              ;; component keyword arg then rendered later).
               (is-render-expr? expr)
-                (render-expr expr env)
+                (make-raw-html (render-expr expr env))
 
               ;; Fall through to function call
               :else (eval-call head args env)))