Creates Oban's tables for the standalone test database.

Oban's schema is not an Ash resource, so mix ash.codegen never emits it — and the migrations this extension does generate are a build artifact that is deliberately not committed. Rather than hand-write a migration into priv/, the harness runs this one at boot (MishkaCmsCore.Test.Boot), which keeps the generated-only rule intact and leaves nothing to check in.

A host application supplies these tables itself; this exists only so the runtime workers this library owns have somewhere to enqueue while they are being tested on their own.