Add ServerSessionT type var to Context (#271)

* Add ServerSessionT type var to Context

* Passing locally

* Try now

src/mcp/server/session.py

@@ -38,7 +38,7 @@ be instantiated directly by users of the MCP framework.
 """
 
 from enum import Enum
-from typing import Any
+from typing import Any, TypeVar
 
 import anyio
 import anyio.lowlevel
@@ -59,6 +59,9 @@ class InitializationState(Enum):
     Initialized = 3
 
 
+ServerSessionT = TypeVar("ServerSessionT", bound="ServerSession")
+
+
 class ServerSession(
     BaseSession[
         types.ServerRequest,