enhance: improve AsyncMilvusClient connection error message (#3102)

Provide user-friendly error message with solutions and examples when
AsyncMilvusClient is called from sync context without event loop.

also see #3099

Signed-off-by: silas.jiang <[email protected]>
Co-authored-by: silas.jiang <[email protected]>

Author: jac0626

pymilvus/milvus_client/_utils.py

@@ -2,6 +2,7 @@
 import hashlib
 import logging
 
+from pymilvus.exceptions import ConnectionConfigException
 from pymilvus.orm.connections import connections
 
 logger = logging.getLogger(__name__)
@@ -38,8 +39,12 @@ def create_connection(
         # reusing connections from closed event loops
         loop_id_fmt = ""
         if use_async:
-            loop = asyncio.get_running_loop()
-            loop_id_fmt = f"loop{id(loop)}"
+            try:
+                loop = asyncio.get_running_loop()
+                loop_id_fmt = f"loop{id(loop)}"
+            except RuntimeError as e:
+                error_msg = "Cannot create async connection: no running event loop. Please ensure you are running in an async context."
+                raise ConnectionConfigException(message=error_msg) from e
 
         # different uri, auth, db_name, and event loop (for async) cannot share the same connection
         not_empty = [v for v in [use_async_fmt, uri, db_name, auth_fmt, loop_id_fmt] if v]