add global context for session (flet-dev#2934)

* add global context for session

* export context

sdk/python/packages/flet-core/src/flet_core/page.py

@@ -523,6 +523,7 @@ def wrapper(*args, **kwargs):
         return wrapper
 
     def run_task(self, handler: Callable[..., Awaitable[Any]], *args, **kwargs):
+        _session_page.set(self)
         assert asyncio.iscoroutinefunction(handler)
 
         handler_with_context = self.__context_wrapper(handler)
@@ -543,6 +544,13 @@ def _on_completion(f):
 
         return future
 
+    def __context_wrapper(self, handler):
+        def wrapper(*args):
+            _session_page.set(self)
+            handler(*args)
+
+        return wrapper
+
     def run_thread(self, handler, *args):
         handler_with_context = self.__context_wrapper(handler)
         if is_pyodide():