storage: read non-pruned blocks with fewer DB reads

[redsh4de]

What

read non-pruned blocks tx blobs in one big read, like the pruned ones

Why

3-4 tape reads instead of 2 * (tx count) + 1

Where

storage

How

• move the big bulk read out of the pruned branch so it applies for both pruned & non-pruned
• non-pruned also reads each prunable tape (v1/v2) once, then stitches pruned + prunable per tx
• add read_blob helper to keep things DRY