fix: add BaseExceptionGroup compat import to session.py + sort test imports

Author: g97iulio1609

src/mcp/shared/session.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import logging
+import sys
 from collections.abc import Callable
 from contextlib import AsyncExitStack
 from types import TracebackType
@@ -11,6 +12,9 @@
 from pydantic import BaseModel, TypeAdapter
 from typing_extensions import Self
 
+if sys.version_info < (3, 11):
+    from exceptiongroup import BaseExceptionGroup
+
 from mcp.shared._exception_utils import collapse_exception_group
 from mcp.shared.exceptions import MCPError
 from mcp.shared.message import MessageMetadata, ServerMessageMetadata, SessionMessage

tests/shared/test_exception_utils.py

@@ -2,9 +2,8 @@
 
 import sys
 
-import pytest
-
 import anyio
+import pytest
 
 if sys.version_info < (3, 11):
     from exceptiongroup import BaseExceptionGroup