Add missing get_transaction from async session (#186)

* Add missing get_transaction from async session

Fixes: #185

* also add get_nested_transcation

Author: CaselIT

sqlalchemy-stubs/ext/asyncio/session.pyi

@@ -244,6 +244,8 @@ class AsyncSession(
     async def __aexit__(
         self, type_: Any, value: Any, traceback: Any
     ) -> None: ...
+    def get_transaction(self) -> Optional[AsyncSessionTransaction]: ...
+    def get_nested_transaction(self) -> Optional[AsyncSessionTransaction]: ...
 
 class _AsyncSessionContextManager:
     async_session: AsyncSession = ...

test/files/async_stuff.py

@@ -29,3 +29,10 @@ async def go() -> None:
         cr.first()
         scr = await conn.stream_scalars(text("select 1"))
         await scr.all()
+
+    ast = async_session.get_transaction()
+    if ast:
+        ast.is_active
+    nt = async_session.get_nested_transaction()
+    if nt:
+        nt.is_active