Use getBlobs info to estimate private blobs

The slot info tab gives a view of getBlobs request times + how many blobs it fetched.

<img width="540" height="683" alt="Image" src="https://github.com/user-attachments/assets/2680130f-cac0-46a7-b289-0be62ad9b162" />

Can we use this info to also have a field like `hasPrivateBlobs` on the slot which is true if all ELs returned 0 blobs and the block has >0 blobs?