Fix sync for folders synced by earlier versions

[const-cloudinary]

Since #124, sync adds the extension to the remote name of a raw file in dynamic folder mode (notes → notes.txt). Local folders synced by earlier versions still use the old names, so sync --push treated those remote files as unique and deleted them.

Use cases fixed

Case	Before this PR	After
Raw file pushed by an earlier version (.cld-sync has notes.txt → notes)	Every second push deletes the remote file and uploads nothing	In sync
Raw files with the same base name pushed by an earlier version (notes.txt, notes.csv)	Push deletes both remote files and uploads nothing	In sync
Raw file pulled by an earlier version (local notes, no extension)	Push deletes the remote file and uploads the local file again, without the extension and with a new public ID	In sync
Raw duplicates pulled by an earlier version (notes (1), notes (2), ...), including after a remote copy was deleted	Push deletes all remote copies and uploads them again with new public IDs	Matched by content, nothing deleted
Any .cld-sync entry that points to a remote file that no longer exists, for images too (e.g. a.png → zzz.png while a.png is on Cloudinary)	Push deletes a.png and uploads nothing	In sync

Brief Summary of Changes

• SyncDir._verify_diverse_file_names (cloudinary_cli/modules/sync.py), applied when .cld-sync is read:
  • Drops entries whose remote file does not exist.
  • In dynamic folder mode, maps an unmatched remote raw file to a local file named after its display name without the extension (notes, notes (1), ...), only when the content (etag) is the same.
• delete_cld_folder_if_exists (test/helper_test.py) deletes test assets of all resource types. It deleted only images before.
• 4 integration tests in TestCLISync, dynamic folder mode only. One per row above, except the last, plus one for a new push and pull of a raw file.

What does this PR address?

• GitHub issue (Add reference - #XX)
• Refactoring
• New feature
• Bug fix
• Adds more tests

Are tests included?

• Yes
• No

Reviewer, please note:

• No change for images and videos, or in fixed folder mode, other than dropping .cld-sync entries that point to missing files. When the target is missing, keeping the entry and dropping it give the same result for push and pull.
• A local file is matched with a remote raw file only when the content is the same. Otherwise sync works as on master.
• Checked against a test cloud on master and on this branch, with the same results for images and videos:
  • the image test folder in dynamic and fixed folder mode (push, push, pull into an empty folder, push);
  • videos with duplicate names;
  • an image and a raw file with the same base name;
  • the jpeg alias.

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I ran the full test suite before pushing the changes and all the tests pass.

Ran the sync tests only: test/test_modules/test_cli_sync.py, 13 existing integration tests, 4 new ones, and 6 offline ones, all passing.

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