Address schema support

For multi-clusters access, most distributed file systems support address schema:

```
hdfs://localhost:9999/path/to/a/file
```

I wonder if BFS could support address schema for the convenience of cluster cross access. Especially in SDK, `list` interface could return a list of formatted address.

Start by reading the SDK's `list` interface and the issue's example address format. Clarify how cluster addresses should be represented and whether cross-cluster paths are in scope; completion should include support for formatted addresses such as `hdfs://localhost:9999/path/to/a/file`.

Written by the indexing model from the issue text.