fix(Mistral): default tool call type to function for Mistral compatibility (#744)

The Mistral API currently omits the `type` attribute in its tool call
responses, which causes an `Undefined array key "type"` exception.
This commit defaults the missing `type` to `'function'` (the standard
supported type per OpenAI documentation) to prevent runtime errors
and ensure broader compatibility with OpenAI-compatible APIs.

Fixes #397

Author: ivanmestre

src/Responses/Chat/CreateResponseToolCall.php

@@ -13,13 +13,13 @@ private function __construct(
     ) {}
 
     /**
-     * @param  array{id: string, type: string, function: array{name: string, arguments: string}}  $attributes
+     * @param  array{id: string, type?: string, function: array{name: string, arguments: string}}  $attributes
      */
     public static function from(array $attributes): self
     {
         return new self(
             $attributes['id'],
-            $attributes['type'],
+            $attributes['type'] ?? 'function',
             CreateResponseToolCallFunction::from($attributes['function']),
         );
     }