Fix incorrect image URL formation when using separate name and tag parameters
where the tag contains a digest. Previously, tags like "8-bookworm@sha256:..."
would incorrectly use "@" as the delimiter between name and tag, resulting in
malformed URLs like "docker.io/valkey/valkey@8-bookworm@sha256:...".
The issue was in ImageRepository.delimiter logic which used substring matching
("sha256" in tag) instead of checking for pure digest format.
Changes:
- Fix delimiter selection in ImageRepository.__init__() to only use "@" for
pure digests starting with "sha256:", not any tag containing "sha256"
- Add comprehensive unit tests covering all delimiter scenarios
- Add integration tests with real digest validation and edge cases
- Ensure proper URL formation: name:tag@digest vs name@digest
Before: docker.io/valkey/valkey@8-bookworm@sha256:abc123 (broken)
After: docker.io/valkey/valkey:8-bookworm@sha256:abc123 (correct)
Fixes#947
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Signed-off-by: Sagi Shnaidman <sshnaidm@redhat.com>
