Checkpointing of FuncX Task Server

[WardLT]

FuncX keeps track of the state of a task in the cloud, which means that we could shutdown a task server and then re-initialize it without loosing any information. Problem is, we don't currently support this and need to work out a few things:

• Whether we can associate a series of tasks with a single identifier (e.g., the name of a Colmena run)
• If not, developing a mechanism to save task ids associated with a run locally