fix: get_event_loop - set new loop as current loop in threads (#40)

a_sync/_helpers.py

@@ -14,11 +14,13 @@
 
 def get_event_loop() -> asyncio.BaseEventLoop:
     try:
-        return asyncio.get_event_loop()
+        loop = asyncio.get_event_loop()
     except RuntimeError as e: # Necessary for use with multi-threaded applications.
         if not str(e).startswith("There is no current event loop in thread"):
             raise e
-        return asyncio.new_event_loop()
+        loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(loop)
+    return loop
 
 def _validate_wrapped_fn(fn: Callable) -> None:
     """Ensures 'fn' is an appropriate function for wrapping with a_sync."""