v0.6.0-rc.4

What's Changed

• fix: serde for sql request by @geofmureithi in #371
• fix: handle attempts in storages by @geofmureithi in #373
• add: test utils that allow backend polling during tests by @geofmureithi in #374
• bump: to 0.6.0-rc.4 by @geofmureithi in #377

Full Changelog: v0.6.0-rc.3...v0.6.0-rc.4