Release v0.20.0

What's Changed

• Special steps runAsTxn by @maxdml in #380
• Fix a getEvent bug and re-design the notification subscription system by @maxdml in #382
• Queryable schedule names & scheduler direct enqueue by @maxdml in #383
• Fix step cancellation outcome by @maxdml in #384
• Fix deadlock and sqlite err propagation by @maxdml in #389
• Subpackages by @maxdml in #390
• Fixes by @maxdml in #391
• Distinguish between our own checkpointing writes and conflicting writes by @maxdml in #392
• fix: apply schedule race condition by @toastsandwich in #386
• Warn error cause lost by @maxdml in #393

Full Changelog: v0.19.0...v0.20.0