feat(manager): Make the manager responsible for saving the tasks.

[VoyTechnology]

This change adds a empty state store which does nothing. It is not yet fully decided what component should be storing the state, so the default is changed for the worker do not save any data.

The role of saving the progress of tasks falls onto manager.

[GoldenBadger]

You can remove this and remove the return keywords in the match statement for brevity.

[GoldenBadger]

all of these can be removed if you remove the semicolon on the previous lines

[VoyTechnology]

I get the following error when I do this:

error[E0308]: match arms have incompatible types
   --> manager/src/state/file.rs:138:17
    |
138 | /                 File::create(pending_file_path)
139 | |                     .context(StateErrorKind::PendingTaskWriteFailed)?
140 | |                     .write_all(&task_id.as_bytes())
141 | |                     .context(StateErrorKind::PendingTaskWriteFailed)?
    | |_____________________________________________________________________^ expected enum `std::result::Result`, found ()
    |
    = note: expected type `std::result::Result<(), state::StateError>`
               found type `()`

[VoyTechnology]

Would I just wrap the whole statement in Ok(...)?