Fix: Artifact pull failing when running cmf init ssh

[AyeshaSanadi]

Related Issues / Pull Requests

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Description

Include a brief summary of the proposed changes.

What changes are proposed in this pull request?

• The original code used sftp.put() (which uploads to remote) instead of sftp.get() (which downloads from remote). Fixed in both download_file and download_directory.
• Wrong variable in download_directory inner loop: Original passed object_name (the .dir manifest path) to sftp.put() for every file instead of temp_object_name (the individual file's content-addressed path).
• Size integrity check fixed in download_file: Original used os.stat(object_name).st_size — a local stat() on a remote path string, which would fail. Fixed to use remote stat before download and local stat after.
• Connection reuse via _get_connection() + auto-close via __del__.

Checklist:

• My code follows the style guidelines of this project (PEP-8 with Google-style docstrings).
• My code modifies existing public API, or introduces new public API, and I updated or wrote docstrings that
  uses Google-style formatting and any other formatting that is supported by mkdocs and plugins this project
  uses.
• I have commented my code.
• My code requires documentation updates, and I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.