misc: simplify running non-async callback using asyncio.to_thread (#1661)

* refactor: simplify running non-async callback using asyncio.to_thread

* add changes

CHANGES/1661.misc.rst

@@ -0,0 +1 @@
+Replaced ```loop.run_in_executor``` with ```asyncio.to_thread``` for improved readability and consistency.

aiogram/dispatcher/event/handler.py

@@ -41,11 +41,7 @@ class CallableObject:
         wrapped = partial(self.callback, *args, **self._prepare_kwargs(kwargs))
         if self.awaitable:
             return await wrapped()
-
-        loop = asyncio.get_event_loop()
-        context = contextvars.copy_context()
-        wrapped = partial(context.run, wrapped)
-        return await loop.run_in_executor(None, wrapped)
+        return await asyncio.to_thread(wrapped)
 
 
 @dataclass