fix: add comprehensive type annotations to test fixture

- Add type aliases for stream types to improve clarity

- Add return type annotation to fixture

- Add type hints to internal _create function

- Fixes all pyright type checking errors

Author: dgenio

tests/shared/test_proxy.py

@@ -1,19 +1,29 @@
 """Tests for the MCP proxy pattern."""
 
+from collections.abc import Callable
+
 import anyio
 import pytest
+from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 
 from mcp.shared.message import SessionMessage
 from mcp.shared.proxy import mcp_proxy
 from mcp.types import JSONRPCMessage, JSONRPCRequest
 
+# Type aliases for clarity
+ReadStream = MemoryObjectReceiveStream[SessionMessage | Exception]
+WriteStream = MemoryObjectSendStream[SessionMessage]
+StreamPair = tuple[ReadStream, WriteStream]
+WriterReaderPair = tuple[MemoryObjectSendStream[SessionMessage | Exception], MemoryObjectReceiveStream[SessionMessage]]
+StreamsFixtureReturn = tuple[StreamPair, StreamPair, WriterReaderPair, WriterReaderPair]
+
 
 @pytest.fixture
-async def create_streams():
+async def create_streams() -> Callable[[], StreamsFixtureReturn]:
     """Helper fixture to create memory streams for testing with proper cleanup."""
-    streams_to_cleanup = []
+    streams_to_cleanup: list[MemoryObjectSendStream[SessionMessage | Exception] | MemoryObjectReceiveStream[SessionMessage | Exception] | MemoryObjectSendStream[SessionMessage] | MemoryObjectReceiveStream[SessionMessage]] = []
 
-    def _create():
+    def _create() -> StreamsFixtureReturn:
         client_read_writer, client_read = anyio.create_memory_object_stream[SessionMessage | Exception](10)
         client_write, client_write_reader = anyio.create_memory_object_stream[SessionMessage](10)