OPFS Blockstore

[lidel]

In spare time we should explore if there is a benefit in replacing IndexedDB-backed block storage with blockstore-opfs (in theory avoids structured clone overhead but the diff could be negligible)

[achingbrain]

The blockstore is only active during the initial content load by the service worker, after that all responses are served from the browser's response cache, TBH we barely need a blockstore at all and can probably swap it out for a BlackHoleBlockstore that doesn't store anything.