Images included in pasted HTML are not uploaded as attachments, and inline ones are lost

Steps to reproduce

1. create a page A, attach an image to it and insert that image in its content
2. add a second paragraph to page A containing an image inline inside the text
3. save page A and view it
4. open a page B in edit mode, with the BlockNote editor
5. in page A's view mode, select everything and copy
6. paste into the BlockNote editor of page B
7. save page B

Expected result

• both images are attached to page B and referenced from its content as [[image:image.png]]

Actual result

• the block-level image is inserted as an external URL image, still pointing at page A's attachment. Nothing is attached to page B, so page A has no way of knowing that another page references its attachment, and the image breaks as soon as page A or its attachment is removed.
• the inline image is silently dropped: no image, no external URL image, no warning

Cause

BlockNote only calls the uploadFile callback when the clipboard or the drop carries a Files entry:

// @blocknote/core, handleFileInsertion
if (i !== "Files") return;

Content copied from a web page arrives as text/html, so that path is never taken and the <img src> of the pasted HTML is inserted as-is. The uploadFile callback added by XWIKI-24758 only ever sees the files dropped from the file manager or pasted from a screenshot tool.

Attaching the referenced images needs a pass over the pasted HTML that fetches each external image, attaches it to the edited page and rewrites the reference.

Notes

• This is the BlockNote counterpart of XWIKI-20350 and XWIKI-22611, which fixed the same problem for CKEditor.
• Reproduced on master as well.