feat(core): Wrap cron withMonitor callback in withIsolationScope

[timfish]

Multiple cron jobs can run at the same time and they may run on a server where other work is being performed.

Wrapping the withMonitor callback in withIsolationScope ensures that scope and breadcrumbs for the cron tasks remain isolated.

[mydea]

this makes sense to me!

Maybe (can be in a follow up) we can add one or two tests for this, ensuring crons are properly isolated 🤔

[timfish]

we can add one or two tests for this

I was actually in the middle of writing cron tests when I got distracted by isolation!