Improve generic backend test suite for query api

[Johnabell]

Currently there is some coverage of the query API and prune API in the rexecutor::backend::testing::test_suite! macro, however it does not cover all the cases such as

• pruning scheduled/retryable jobs correct behaviour is should prune jobs furthest in future.
• Query::Or
• Query::DataEquals
• Query::MetadataEquals
• Query::IdIn
• Query::StatusEqual
• Query::TagsAllOf
• Query::ScheduledAtBefore
• Query::ScheduledAtAfter