feat: basic cachew CLI

[alecthomas]

The CLI includes direct low-level operations, and two high level operations for snapshotting and restoring directories using tar+zstd:

Usage: cachew <command> [flags]

Flags:
  -h, --help                           Show context-sensitive help.
      --log-json                       Enable JSON logging ($CACHEW_LOG_JSON).
      --log-level=info                 Set the logging level ($CACHEW_LOG_LEVEL).
      --url="http://127.0.0.1:8080"    Remote cache server URL ($CACHEW_URL).
      --platform                       Prefix keys with platform (${os}-${arch}-) ($CACHEW_PLATFORM).

Operations:
  get       Download object from cache.
  stat      Show metadata for cached object.
  put       Upload object to cache.
  delete    Remove object from cache.

Snapshots:
  snapshot    Create compressed archive of directory and upload.
  restore     Download and extract archive to directory.

Run "cachew <command> --help" for more information on a command.