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

uv.lock

@@ -163,7 +163,7 @@ wheels = [
 
 [[package]]
 name = "mcp-python"
-version = "0.3.0.dev0"
+version = "0.5.0.dev0"
 source = { editable = "." }
 dependencies = [
     { name = "anyio" },