refactor: extract MdrsClient service layer for library portability

To improve the tool's portability as a Python library, the core logic
has been decoupled from the CLI interface. This allows developers to
programmatically interact with MDRS without relying on CLI-specific
argument parsing or local file-based caches.

- Introduce `MdrsClient` service layer to handle core operations.
- Abstract authentication state using `CacheInterface` and `InMemoryCache`.
- Migrate all CLI commands to utilize `MdrsClient` for execution.
- Separate `Doi` data model from API responses and move to `models/doi.py`.
- Update `README.md` to include Python API usage examples.
- Bump package version to 1.3.17.

mdrsclient/commands/whoami.py

@@ -23,12 +23,15 @@ class WhoamiCommand(BaseCommand):
 
     @classmethod
     def whoami(cls, remote: str) -> None:
-        remote = cls._parse_remote_host(remote)
-        config = ConfigFile(remote)
-        if config.url is None:
-            raise MissingConfigurationException(f"Remote host `{remote}` is not found.")
-        connection = MDRSConnection(config.remote, config.url)
-        if connection.token is not None and connection.token.is_expired:
-            connection.logout()
-        username = connection.user.username if connection.user is not None else cls.ANONYMOUS_USERNAME
+        remote_host = cls._parse_remote_host(remote)
+        from mdrsclient.client import MdrsClient
+
+        client = MdrsClient.from_remote(remote_host)
+        if client.connection.token is not None and client.connection.token.is_expired:
+            client.logout()
+        try:
+            user = client.whoami()
+            username = user.username if user is not None else cls.ANONYMOUS_USERNAME
+        except Exception:
+            username = cls.ANONYMOUS_USERNAME
         print(username)