feat: speed up SmartTask and SmartFuture init

a_sync/_smart.py

@@ -6,6 +6,7 @@
 """
 
 import asyncio
+import contextvars
 import logging
 import warnings
 import weakref
@@ -197,7 +198,7 @@ def __init__(
         if key:
             self._key = key
         self._waiters = weakref.WeakSet()
-        self.add_done_callback(SmartFuture._self_done_cleanup_callback)
+        self._callbacks.append((SmartFuture._self_done_cleanup_callback, contextvars.copy_context()))
 
     def __repr__(self):
         return f"<{type(self).__name__} key={self._key} waiters={self.num_waiters} {self._state}>"
@@ -298,7 +299,7 @@ def __init__(
         """
         asyncio.Task.__init__(self, coro, loop=loop, name=name)
         self._waiters: Set["asyncio.Task[T]"] = set()
-        self.add_done_callback(SmartTask._self_done_cleanup_callback)
+        self._callbacks.append((SmartTask._self_done_cleanup_callback, contextvars.copy_context()))
 
 
 def smart_task_factory(