[Feature] Support Models in dbutils.fs operations (#750)

## Changes
<!-- Summary of your changes that are easy to understand -->
- Support files operations in WorkspaceClient.Files for Databricks UC
Model artifacts so that user can use databricks sdk to download UC model
artifacts.
- This PR is part of the work to migrate mlflow client towards using
databricks sdk for model artifacts download/upload operations for better
security.

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->
- Existing tests in test_dbfs_mixins.py, similar to how _VolumesPath is
tested
- The following code works
```
from databricks.sdk import WorkspaceClient
w = WorkspaceClient()
resp = w.files.download("/Models/system/ai/dbrx_instruct/3/MLmodel")
```

- [x] `make test` run locally
- [x] `make fmt` applied
- [x] relevant integration tests applied

databricks/sdk/mixins/files.py

@@ -167,7 +167,7 @@ def __repr__(self) -> str:
         return f"<_DbfsIO {self._path} {'read' if self.readable() else 'write'}=True>"
 
 
-class _VolumesIO(BinaryIO):
+class _FilesIO(BinaryIO):
 
     def __init__(self, api: files.FilesAPI, path: str, *, read: bool, write: bool, overwrite: bool):
         self._buffer = []
@@ -262,7 +262,7 @@ def __exit__(self, __t, __value, __traceback):
         self.close()
 
     def __repr__(self) -> str:
-        return f"<_VolumesIO {self._path} {'read' if self.readable() else 'write'}=True>"
+        return f"<_FilesIO {self._path} {'read' if self.readable() else 'write'}=True>"
 
 
 class _Path(ABC):
@@ -398,7 +398,7 @@ def __repr__(self) -> str:
         return f'<_LocalPath {self._path}>'
 
 
-class _VolumesPath(_Path):
+class _FilesPath(_Path):
 
     def __init__(self, api: files.FilesAPI, src: Union[str, pathlib.Path]):
         self._path = pathlib.PurePosixPath(str(src).replace('dbfs:', '').replace('file:', ''))
@@ -411,7 +411,7 @@ def _is_dbfs(self) -> bool:
         return False
 
     def child(self, path: str) -> Self:
-        return _VolumesPath(self._api, str(self._path / path))
+        return _FilesPath(self._api, str(self._path / path))
 
     def _is_dir(self) -> bool:
         try:
@@ -431,7 +431,7 @@ def exists(self) -> bool:
             return self.is_dir
 
     def open(self, *, read=False, write=False, overwrite=False) -> BinaryIO:
-        return _VolumesIO(self._api, self.as_string, read=read, write=write, overwrite=overwrite)
+        return _FilesIO(self._api, self.as_string, read=read, write=write, overwrite=overwrite)
 
     def list(self, *, recursive=False) -> Generator[files.FileInfo, None, None]:
         if not self.is_dir:
@@ -458,13 +458,13 @@ def list(self, *, recursive=False) -> Generator[files.FileInfo, None, None]:
     def delete(self, *, recursive=False):
         if self.is_dir:
             for entry in self.list(recursive=False):
-                _VolumesPath(self._api, entry.path).delete(recursive=True)
+                _FilesPath(self._api, entry.path).delete(recursive=True)
             self._api.delete_directory(self.as_string)
         else:
             self._api.delete(self.as_string)
 
     def __repr__(self) -> str:
-        return f'<_VolumesPath {self._path}>'
+        return f'<_FilesPath {self._path}>'
 
 
 class _DbfsPath(_Path):
@@ -589,8 +589,8 @@ def _path(self, src):
                 'UC Volumes paths, not external locations or DBFS mount points.')
         if src.scheme == 'file':
             return _LocalPath(src.geturl())
-        if src.path.startswith('/Volumes'):
-            return _VolumesPath(self._files_api, src.geturl())
+        if src.path.startswith(('/Volumes', '/Models')):
+            return _FilesPath(self._files_api, src.geturl())
         return _DbfsPath(self._dbfs_api, src.geturl())
 
     def copy(self, src: str, dst: str, *, recursive=False, overwrite=False):

tests/test_dbfs_mixins.py

@@ -1,8 +1,8 @@
 import pytest
 
 from databricks.sdk.errors import NotFound
-from databricks.sdk.mixins.files import (DbfsExt, _DbfsPath, _LocalPath,
-                                         _VolumesPath)
+from databricks.sdk.mixins.files import (DbfsExt, _DbfsPath, _FilesPath,
+                                         _LocalPath)
 
 
 def test_moving_dbfs_file_to_local_dir(config, tmp_path, mocker):
@@ -55,11 +55,14 @@ def test_moving_local_dir_to_dbfs(config, tmp_path, mocker):
 
 
 @pytest.mark.parametrize('path,expected_type', [('/path/to/file', _DbfsPath),
-                                                ('/Volumes/path/to/file', _VolumesPath),
+                                                ('/Volumes/path/to/file', _FilesPath),
+                                                ('/Models/path/to/file', _FilesPath),
                                                 ('dbfs:/path/to/file', _DbfsPath),
-                                                ('dbfs:/Volumes/path/to/file', _VolumesPath),
+                                                ('dbfs:/Volumes/path/to/file', _FilesPath),
+                                                ('dbfs:/Models/path/to/file', _FilesPath),
                                                 ('file:/path/to/file', _LocalPath),
-                                                ('file:/Volumes/path/to/file', _LocalPath), ])
+                                                ('file:/Volumes/path/to/file', _LocalPath),
+                                                ('file:/Models/path/to/file', _LocalPath), ])
 def test_fs_path(config, path, expected_type):
     dbfs_ext = DbfsExt(config)
     assert isinstance(dbfs_ext._path(path), expected_type)