Fix return type in abstract methods from self to static (#53)

* Change return type of abstract request methods

* Change return type of `fromParams` method to `static` in request classes

(cherry picked from commit 94799ab66ff60d4b2305aadb6b73aaa4c805221e)

* Make request classes final and update `getParams` return types for improved type safety

(cherry picked from commit d6be496f89cc0e6d30f519792d0dc902685c4178)

src/Schema/Request/CreateSamplingMessageRequest.php

@@ -23,7 +23,7 @@ use Mcp\Schema\ModelPreferences;
  *
  * @author Kyrian Obikwelu <koshnawaza@gmail.com>
  */
-class CreateSamplingMessageRequest extends Request
+final class CreateSamplingMessageRequest extends Request
 {
     /**
      * @param SamplingMessage[]     $messages       the messages to send to the model
@@ -59,7 +59,7 @@ class CreateSamplingMessageRequest extends Request
         return 'sampling/createMessage';
     }
 
-    protected static function fromParams(?array $params): Request
+    protected static function fromParams(?array $params): static
     {
         if (!isset($params['messages']) || !\is_array($params['messages'])) {
             throw new InvalidArgumentException('Missing or invalid "messages" parameter for sampling/createMessage.');
@@ -86,7 +86,19 @@ class CreateSamplingMessageRequest extends Request
         );
     }
 
-    protected function getParams(): ?array
+    /**
+     * @return array{
+     *     messages: SamplingMessage[],
+     *     maxTokens: int,
+     *     preferences?: ModelPreferences,
+     *     systemPrompt?: string,
+     *     includeContext?: string,
+     *     temperature?: float,
+     *     stopSequences?: string[],
+     *     metadata?: array<string, mixed>
+     * }
+     */
+    protected function getParams(): array
     {
         $params = [
             'messages' => $this->messages,