Keep exteneded typings

To be dealt with when dropping support for python 3.8 and 3.9

src/gt4py/eve/extended_typing.py

@@ -73,6 +73,10 @@
         Set as AbstractSet,
         ValuesView as ValuesView,
     )
+    from contextlib import (
+        AbstractAsyncContextManager as AsyncContextManager,
+        AbstractContextManager as ContextManager,
+    )
     from re import Match as Match, Pattern as Pattern