[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/RequestHandler/ListPromptsHandler.php

@@ -1,53 +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\RequestHandler;
-
-use Mcp\Capability\Registry\ReferenceProviderInterface;
-use Mcp\Exception\InvalidCursorException;
-use Mcp\Schema\JsonRpc\HasMethodInterface;
-use Mcp\Schema\JsonRpc\Response;
-use Mcp\Schema\Request\ListPromptsRequest;
-use Mcp\Schema\Result\ListPromptsResult;
-use Mcp\Server\MethodHandlerInterface;
-use Mcp\Server\Session\SessionInterface;
-
-/**
- * @author Tobias Nyholm <tobias.nyholm@gmail.com>
- */
-final class ListPromptsHandler implements MethodHandlerInterface
-{
-    public function __construct(
-        private readonly ReferenceProviderInterface $registry,
-        private readonly int $pageSize = 20,
-    ) {
-    }
-
-    public function supports(HasMethodInterface $message): bool
-    {
-        return $message instanceof ListPromptsRequest;
-    }
-
-    /**
-     * @throws InvalidCursorException
-     */
-    public function handle(ListPromptsRequest|HasMethodInterface $message, SessionInterface $session): Response
-    {
-        \assert($message instanceof ListPromptsRequest);
-
-        $page = $this->registry->getPrompts($this->pageSize, $message->cursor);
-
-        return new Response(
-            $message->getId(),
-            new ListPromptsResult($page->references, $page->nextCursor),
-        );
-    }
-}