fix(e2core): Deal with dead processes

[javorszky]

Related to #426

This is a quality of life improvement that deals with crashed processes and recovery.

When using the command.Start() function call, the process starts in the background. We're supposed to use the command.Wait() to determine when either the process finished, or exited for some other reason.

This changeset accommodates collecting the wait functions, starts them for each sub process, and when they unblock, their ports are added to a died map, which will then be removed automatically from watcher's bookkeeping.

I've tested this manually by:

1. creating an image for e2core using make docker/dev
2. starting up everything with se2's docker compose up (this is internal)
3. start following the logs with docker compose logs e2core --follow (this is internal)
4. making sure that I can execute an existing function
5. hopping into the e2core docker container with docker exec -i -t a063f35d5c2b /bin/bash where the a06... is the image ID you get if you list the images with docker ps for e2core
6. once inside, listing the process IDs with ls -l /proc/*/exe, which will have a similar output:

   lrwxrwxrwx 1 e2core e2core 0 May  3 17:20 /proc/1/exe -> /usr/local/bin/e2core
   lrwxrwxrwx 1 e2core e2core 0 May  3 17:21 /proc/16/exe -> /usr/local/bin/e2core
   lrwxrwxrwx 1 e2core e2core 0 May  3 17:31 /proc/38/exe -> /bin/bash
   lrwxrwxrwx 1 e2core e2core 0 May  3 17:33 /proc/self/exe -> /bin/ls
   lrwxrwxrwx 1 e2core e2core 0 May  3 17:33 /proc/thread-self/exe -> /bin/ls
   

7. of those, the second e2core is the sub process with process id 16
8. kill -9 16 to terminate that
9. look at the logs to see that the termination and reaping of instance was completed and a new one was started during reconcile step
10. check again that I can execute the same function by sending the post request to the local edge endpoint

[ospencer]

LGTM. I would probably call it a dead list instead of a died list, but that's not enough for me to block this change.

[javorszky]

I would probably call it a dead list instead of a died list

heck yeah smple past vs past participle! lemme change that around, it's smol effort