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

mcp_python/client/session.py

@@ -1,3 +1,5 @@
+from datetime import timedelta
+
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from pydantic import AnyUrl
 
@@ -36,8 +38,15 @@ class ClientSession(
         self,
         read_stream: MemoryObjectReceiveStream[JSONRPCMessage | Exception],
         write_stream: MemoryObjectSendStream[JSONRPCMessage],
+        read_timeout_seconds: timedelta | None = None,
     ) -> None:
-        super().__init__(read_stream, write_stream, ServerRequest, ServerNotification)
+        super().__init__(
+            read_stream,
+            write_stream,
+            ServerRequest,
+            ServerNotification,
+            read_timeout_seconds=read_timeout_seconds,
+        )
 
     async def initialize(self) -> InitializeResult:
         from mcp_python.types import (