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/mkdir.py

@@ -23,15 +23,8 @@ class MkdirCommand(BaseCommand):
 
     @classmethod
     def mkdir(cls, remote_path: str) -> None:
-        remote, laboratory_name, r_path = cls._parse_remote_host_with_path(remote_path)
-        r_path = r_path.rstrip("/")
-        r_dirname = os.path.dirname(r_path)
-        r_basename = os.path.basename(r_path)
-        connection = cls._create_connection(remote)
-        laboratory = cls._find_laboratory(connection, laboratory_name)
-        parent_folder = cls._find_folder(connection, laboratory, r_dirname)
-        files = cls._find_files(connection, parent_folder.id)
-        if parent_folder.find_sub_folder(r_basename) is not None or find_file(files, r_basename) is not None:
-            raise IllegalArgumentException(f"Cannot create folder `{r_path}`: File exists.")
-        folder_api = FoldersApi(connection)
-        folder_api.create(normalize("NFC", r_basename), parent_folder.id)
+        remote = remote_path.split(":", 1)[0] if ":" in remote_path else ""
+        from mdrsclient.client import MdrsClient
+
+        client = MdrsClient.from_remote(remote)
+        client.mkdir(remote_path)