[Server] Reorganize server handlers and transport structure for better organization (#86)

* refactor: reorganize server handlers and transport structure

* feat: move the test files to corresponding directories

* fix: linter issues

* fix: correct PHPDoc formatting and streamline handler imports

* refactor: update import statement for ServerBuilder to Builder

src/Server/TransportInterface.php

@@ -1,68 +0,0 @@
-<?php
-
-/*
- * This file is part of the official PHP MCP SDK.
- *
- * A collaboration between Symfony and the PHP Foundation.
- *
- * For the full copyright and license information, please view the LICENSE
- * file that was distributed with this source code.
- */
-
-namespace Mcp\Server;
-
-use Symfony\Component\Uid\Uuid;
-
-/**
- * @author Christopher Hertel <mail@christopher-hertel.de>
- * @author Kyrian Obikwelu <koshnawaza@gmail.com>
- */
-interface TransportInterface
-{
-    /**
-     * Initializes the transport.
-     */
-    public function initialize(): void;
-
-    /**
-     * Registers a callback that will be invoked whenever the transport receives an incoming message.
-     *
-     * @param callable(string $message, ?Uuid $sessionId): void $listener The callback function to execute when the message occurs
-     */
-    public function onMessage(callable $listener): void;
-
-    /**
-     * Starts the transport's execution process.
-     *
-     * - For a blocking transport like STDIO, this method will run a continuous loop.
-     * - For a single-request transport like HTTP, this will process the request
-     *   and return a result (e.g., a PSR-7 Response) to be sent to the client.
-     *
-     * @return mixed the result of the transport's execution, if any
-     */
-    public function listen(): mixed;
-
-    /**
-     * Sends a raw JSON-RPC message string back to the client.
-     *
-     * @param string               $data    The JSON-RPC message string to send
-     * @param array<string, mixed> $context The context of the message
-     */
-    public function send(string $data, array $context): void;
-
-    /**
-     * Registers a callback that will be invoked when a session needs to be destroyed.
-     * This can happen when a client disconnects or explicitly ends their session.
-     *
-     * @param callable(Uuid $sessionId): void $listener The callback function to execute when destroying a session
-     */
-    public function onSessionEnd(callable $listener): void;
-
-    /**
-     * Closes the transport and cleans up any resources.
-     *
-     * This method should be called when the transport is no longer needed.
-     * It should clean up any resources and close any connections.
-     */
-    public function close(): void;
-}