Fix the issue of cancelling jobs

[moyodiallo]

A job from the scheduler was not cancelled after its switch was off. After auto-cancelling lot of jobs in OCaml-CI, the solver-service get stuck and can't start solving new request until finish the oldest.

• The structure was :

  • ocluster <--> solver-worker <--> solver-service There was, 3 differents processes communicating via capnp-rpc.

• The new structure is :

  • ocluster <--> solver-worker(solver-service). Now, the solver-worker is in the same process as solver-service, to share a job's switch.

This is part of solving https://github.com/ocurrent/solver-service/issues/53

[moyodiallo]

This is already tested with #52. After the review, we could revert this PR https://github.com/ocurrent/ocaml-ci/pull/768.

[moyodiallo]

Is there any other suggestion before the merge ?

[moyodiallo]

However, it can still be nice to have another review from someone else :)

Thanks for your review, it was very helpful. I don't know how else would be interested for further review.

For extend, I'm cleaning the stress tests https://github.com/ocurrent/solver-service/pull/52 to however would like to test the differences.

cc @tmcgilchrist