WIP: BUG: Support getter's in JupyterLite, Hypha

Discussed in InsightSoftwareConsortium#730.

The result needs to be awaited.

Author: thewtex

docs/jupyterlite/files/Hello3DWorld.ipynb

@@ -8,7 +8,7 @@
    "outputs": [],
    "source": [
     "import piplite\n",
-    "await piplite.install('itkwidgets==1.0a24')"
+    "await piplite.install('itkwidgets==1.0a46.dev18+g0bcf158.d20240111')"
    ]
   },
   {

itkwidgets/viewer.py

@@ -319,7 +319,8 @@ def fetch_value(func: Callable) -> Callable:
         @functools.wraps(func)
         def _fetch_value(self, *args, **kwargs):
             result = func(self, *args, **kwargs)
-            if isawaitable(result):
+            global _cell_watcher
+            if isawaitable(result) and _cell_watcher:
                 future = asyncio.ensure_future(result)
                 self.call_getter(future)
                 return future