Consider using a cpuset for sharded alien threads

[rockwotj]

did you consider passing in a cpuset here? that could allow us more flexibility, for example, arranging for all the alien threads to run on dedicated cores, like here:

https://github.com/ceph/ceph/blob/20398601e76a6ff48b3886d10cffdceb68fcafcb/src/crimson/os/alienstore/alien_store.cc#L105-L119

it'd be a minor change in the future, so i don't think it's necessary right now. the more i think about the more a dedicated core(s) makes a lot of sense. communicating through shared memory is cheap but when we pin the transform to a reactor core we have to context switch and suspend the reactor.

Originally posted by @dotnwat in #13056 (comment)

JIRA Link: CORE-1420

[emaxerrno]

woah!!! this is an awesome idea! haha. clever. Didn't occur to me to have this...

you can now have M:N models woah 🤯 - makes total sense. @rockwotj we should add.

great observation @dotnwat

[rockwotj]

We didn't use alien threads for wasm so closing as obsolete