fix: remove maybe_datum view

[Gozala]

Changes here remove complicated joins per @seefeldb findings that creates huge perf wins and same stuff loads goes from 13sec to 675ms on my machine.

I also added a migration scripts that can be used to migrate old db to new one by running it like

deno task migrate ./path/to/db.sqlite

[ellyxir]

looks good to me. reviewed code, ran migration script and it worked, ran common-memory and jumble and it brought down time from 10 sec to 3.4 seconds.