* Disentangle `collect` module from `reply_data`
why:
Now the module visible from `collect` for fetching data is `peer/fetch`
only.
* Merge `SnapPeerHunt` into `collect`
why:
This part needs to be known by `collect`, only
* rename collect => worker
* Dissolve `sync_fetch_xdesc` module into `common`
why:
Descriptor is only used in `common` and `fetch_trie`
* rename `snap/peer` directory => `snap/worker`
* rename `SnapSync` -> `Worker`, `SnapPeer` -> `WorkerBuddy`
* moved `snap/base_desc.nim` -> `snap/worker/worker_desc.nim`
* Unified opaque object ref naming in `worker_desc.nim`
details:
indicated my inheriting module (exactly one, always)
96bb09457e