Add cancellation support to $do and $doV

[nmaguiar]

Summary

• add cancellation-aware oPromise handling so $do/$doV can interrupt running threads and reject the chain
• document the new cancellation flow for $do/$doV in the advanced guide
• add $do and $doV cancellation coverage to the generic automated tests

Testing

• ojob tests/autoTestAll.Generic.yaml (fails: ojob command not available in container)