Fix dangling fd with stdio

[jprendes]

With #260 the stdio fd are dangling in the parent shim process.
Normally redirecting the stdio would clear the fds.
However, the redirection happens in the clone3d child process.
This means that the parent process maintains a dangling cope of the ´fd´s, keps alive by the shim Instances.

The key changes in this PR are:

• Stdio now offers a take method.
• The Instance impls now use stdio.take() for the last executor, giving up ownership of the fds.
• Adds a smoke test that used to hang without this change.

The rest of the changes are general fixes:

• Change the Muxtex in Stdio to an AtomicCell (we need two nested ones to be able to implement ´take´)
• Add timeouts to the tests in CI
• Update the release workflow, which was using the old path of a moved script
• Replace the macro in Stdio with a generic const.
• implement TryFrom<&InstanceConfig<Engine>> for Stdio

[jprendes]

@CaptainVincent , this is an alternative fix to #280.

[Mossaka]

lgtm!

[jprendes]

Rebased to account for #290.
The fact that we now have only one executor simplifies things and we don't need the nested Arc<AtomicCell<...>>.

[jprendes]

@Mossaka @jsturtevant PTAL.
If possible I would like to have this merged before the end of the week.

[jsturtevant]

LGTM, few comments to help my understanding