Use iscoroutinefunction from inspect not asyncio

Python 3.14 will deprecate asyncio.iscoroutinefunction:
python/cpython#122875

inspect.iscoroutinefunction exists since 3.5 and our baseline
is 3.8, so we can just use it unconditionally.

Using a wrapper with @asyncio.coroutine in __get__ wasn't
necessary (the future from asyncio.ensure_future is awaitable,
and the wrapper doesn't do anything asynchronous), so the
logic can be simplified to just call asyncio.ensure_future
(to schedule the task and store the result when it's
available).

Author: encukou

cached_property.py

@@ -4,6 +4,7 @@
 __license__ = "BSD"
 
 from functools import wraps
+from inspect import iscoroutinefunction
 from time import time
 import threading
 import asyncio
@@ -24,21 +25,14 @@ def __get__(self, obj, cls):
         if obj is None:
             return self
 
-        if asyncio.iscoroutinefunction(self.func):
-            return self._wrap_in_coroutine(obj)
+        if iscoroutinefunction(self.func):
+            value = asyncio.ensure_future(self.func(obj))
+        else:
+            value = self.func(obj)
 
-        value = obj.__dict__[self.func.__name__] = self.func(obj)
+        obj.__dict__[self.func.__name__] = value
         return value
 
-    def _wrap_in_coroutine(self, obj):
-        @wraps(obj)
-        def wrapper():
-            future = asyncio.ensure_future(self.func(obj))
-            obj.__dict__[self.func.__name__] = future
-            return future
-
-        return wrapper()
-
 
 class threaded_cached_property:
     """