testing framework for fixtures and automatic rollbacks

[inoas]

... see how ecto does it.
https://www.postgresql.org/docs/current/subxacts.html / https://stackoverflow.com/a/33860302

[inoas]

https://discord.com/channels/768594524158427167/1433767324506259466/1436294651114950656

[inoas]

https://discord.com/channels/768594524158427167/1433767324506259466/1436375298563117077

[inoas]

https://discord.com/channels/768594524158427167/1433767324506259466/1437028768299483217

[inoas]

https://github.com/inoas/gplace/blob/main/server/test/server_test.gleam#L21-L29