HS: js-block return values + worker stub test

Parser: parse-js-block extracts raw JS source by character positions.
Compiler: js-block AST → hs-js-exec call, stores result in it.
Runtime: hs-js-exec creates JS Function, handles promise rejection.
Test runner: host-new-function/host-promise-state natives + promise monkey-patch.

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

lib/hyperscript/runtime.sx

@@ -2588,3 +2588,21 @@
           node
           (walk (hs-node-get node (first keys)) (rest keys)))))
     (hs-line-for (walk (hs-parse-ast src-str) path))))
+
+(define
+  hs-js-exec
+  (fn
+    (param-names js-src bound-args)
+    (let
+      ((js-fn (host-new-function param-names js-src)))
+      (let
+        ((result (host-call-fn js-fn bound-args)))
+        (if
+          (= (host-typeof result) "promise")
+          (let
+            ((state (host-promise-state result)))
+            (if
+              (and state (= (host-get state "ok") false))
+              (raise (host-get state "value"))
+              (if state (host-get state "value") result)))
+          result)))))