Fix wp:image block created for attachments

[akirk]

The code currently produced creates an invalid block:

<!-- wp:image {"id":"10040","sizeSlug":"large"} -->
<figure class="wp-block-image"><img src="https://example.com/wp-content/uploads/sites/4/2024/11/Tusky-Test_1731495973955_M8D7KUL8U8-scaled.jpg" width="2560" height="1920" alt="" class="wp-image-10040"/></figure>
<!-- /wp:image -->

We need to make the id an integer and remove width and height.

<!-- wp:image {"id":10040,"sizeSlug":"large"} -->
<figure class="wp-block-image"><img src="https://example.com/wp-content/uploads/sites/4/2024/11/Tusky-Test_1731495973955_M8D7KUL8U8-scaled.jpg" alt="" class="wp-image-10040"/></figure>
<!-- /wp:image -->