Rollup node/store: compress messages in database

What

This MR compresses messages in the rollup node SQLite store with Zlib.

Why

The messages table accounts for ~ 70% of the disk usage in the store database. Compressing them reduces the total size of the store by ~50%. (For instance, the store for an archive Ghostnet node goes from 14GB to 7GB.) The messages are not accessed excessively often so the added processing time is negligible.

How

Built on top of !15026 (merged).

By defining a generic "compressed" caqti converter based on an encoding.

Note!

This MR should be merged at approximately the same time as !15026 (merged) if we don't want to introduce an additional store migration as the format is not backward compatible.