Decouple and minimize atelet/ateom shared paths

## Problem

Today ateom and atelet compute many per-actor directory paths from `actorUID` through the same `internal/ateompath` package.

Theses directories are only created and wiped by atelet, and the RPC request between atelet/ateom only carries `actorUID` instead of these directory paths so ateom has to recompute the paths on its end.

## Proposal

atelet owns the `actorUID` related paths and passes it in the RPCs. Can wrap them in a message (e.g. `ActorDirs`) and pass it to atelet RPCs.
```
root_dir
bundle_dir
runsc_state_dir
pid_file_dir
checkpoint_dir
restore_dir
durable_dir_volume_mounts_dir
system_info_volume_roots_dir
volumes_dir
```
These directories are read or writes in ateom as a whole. For per-item paths like pid file ateom can still compute from directory+name, both from the request instead of shared path logic.

We still need to keep some shared paths for atelet/ateom: per-ateom directory and socket, the netns name, the credential broker socket and the OLTP socket.