[Server] Handle malformed JSON-RPC input graceful (#412)

* Never let a throwable escape Protocol::processInput()

* Validate payload types in the schema hydration methods

* Stop leaking handler exception messages to the client

tests/Unit/Fixtures/ThrowingRequest.php

@@ -0,0 +1,38 @@
+<?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\Tests\Unit\Fixtures;
+
+use Mcp\Schema\JsonRpc\Request;
+
+/**
+ * Stands in for a message class that fails with an unexpected throwable instead of a proper
+ * InvalidInputMessageException, e.g. through a PHP TypeError caused by an unvalidated payload.
+ *
+ * @author Christopher Hertel <mail@christopher-hertel.de>
+ */
+final class ThrowingRequest extends Request
+{
+    public static function getMethod(): string
+    {
+        return 'test/throwing';
+    }
+
+    protected static function fromParams(?array $params): static
+    {
+        throw new \TypeError('Internal detail that must not leak to the client.');
+    }
+
+    protected function getParams(): ?array
+    {
+        return null;
+    }
+}