Add in-memory transport (#25)

## Goal

Support running an MCP server in the same process as the client, while preserving MCP abstractions.

## Details

1. **(core change)** Adds a new `memory` transport module that enables in-process client-server communication.
This includes:
   - `create_client_server_memory_streams()` to create bidirectional memory streams
   - `create_connected_server_and_client_session()` to establish an in-process client-server connection

3. (minor) Enhances error handling and timeout support:
   - Adds configurable read timeouts to sessions via `read_timeout_seconds` parameter
   - Improves exception handling in the server with a new `raise_exceptions` flag to control whether errors are returned to clients or raised directly
   - Ensures proper cleanup of request context tokens in error cases

4. (minor) Makes server improvements:
   - Adds built-in ping handler support

tests/shared/test_memory.py

@@ -0,0 +1,28 @@
+import pytest
+from typing_extensions import AsyncGenerator
+
+from mcp_python.client.session import ClientSession
+from mcp_python.server import Server
+from mcp_python.shared.memory import (
+    create_connected_server_and_client_session,
+)
+from mcp_python.types import (
+    EmptyResult,
+)
+
+
+@pytest.fixture
+async def client_connected_to_server(
+    mcp_server: Server,
+) -> AsyncGenerator[ClientSession, None]:
+    async with create_connected_server_and_client_session(mcp_server) as client_session:
+        yield client_session
+
+
+@pytest.mark.anyio
+async def test_memory_server_and_client_connection(
+    client_connected_to_server: ClientSession,
+):
+    """Shows how a client and server can communicate over memory streams."""
+    response = await client_connected_to_server.send_ping()
+    assert isinstance(response, EmptyResult)