refactor: reorganize message handling for better type safety and clarity (#239)

* refactor: improve typing with memory stream type aliases

Move memory stream type definitions to models.py and use them throughout
the codebase for better type safety and maintainability.

GitHub-Issue:#201

* refactor: move streams to ParsedMessage

* refactor: update test files to use ParsedMessage

Updates test files to work with the ParsedMessage stream type aliases
and fixes a line length issue in test_201_client_hangs_on_logging.py.

Github-Issue:#201

* refactor: rename ParsedMessage to MessageFrame for clarity

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

* refactor: move MessageFrame class to types.py for better code organization

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

* fix pyright

* refactor: update websocket client to use MessageFrame

Modified the websocket client to work with the new MessageFrame type,
preserving raw message text and properly extracting the root JSON-RPC
message when sending.

Github-Issue:#204

* fix: use NoneType instead of None for type parameters in MessageFrame

🤖 Generated with [Claude Code](https://claude.ai/code)

* refactor: rename root to message

tests/server/test_session.py

@@ -9,7 +9,7 @@ from mcp.server.session import ServerSession
 from mcp.types import (
     ClientNotification,
     InitializedNotification,
-    JSONRPCMessage,
+    MessageFrame,
     PromptsCapability,
     ResourcesCapability,
     ServerCapabilities,
@@ -19,10 +19,10 @@ from mcp.types import (
 @pytest.mark.anyio
 async def test_server_session_initialize():
     server_to_client_send, server_to_client_receive = anyio.create_memory_object_stream[
-        JSONRPCMessage
+        MessageFrame[None]
     ](1)
     client_to_server_send, client_to_server_receive = anyio.create_memory_object_stream[
-        JSONRPCMessage
+        MessageFrame[None]
     ](1)
 
     async def run_client(client: ClientSession):