_stream: use full element name in artifact log/list-contents

[c1assik]

artifact_log() and artifact_list_contents() were keying their result dicts by obj.name, which is just the bare, project-relative element name. For elements loaded across a junction, this drops the owning junction prefix, so e.g. bst artifact list-contents element.bst nested.bst:element.bst would only show one entry, since both targets resolved to the same key.

Use obj._get_full_name() instead, which includes the junction prefix, falling back to the artifact ref for ArtifactElement targets (i.e. when an artifact is referred to by its ref rather than its element name) as before.

Also drops a dead obj.name = {ref: "No artifact cached"} assignment in artifact_list_contents() that was immediately followed by continue and never used.

Add tests covering artifact log and artifact list-contents with a cross-junction element alongside a same-named top-level element.

[nathanwilliams-ct]

Perhaps it would be better if ArtifactElement overrode the _get_full_name method or the __full_name variable, instead of having this awkward condition here?

Suggested change

	name = ref if isinstance(obj, ArtifactElement) else obj._get_full_name()
	name = obj._get_full_name()

In ArtifactElement

def _get_full_name(self)
   return self.get_artifact_name()

[c1assik]

Added a method _get_full_name() to ArtifactElement.

return self.get_artifact_name(), unconditionally fails with AssertionError: assert key is not None in get_artifact_name() so if the cache key isn't set yet, fall back to super()._get_full_name() (the base Plugin/Element name, which is always safe since it's precomputed earlier in Plugin.init). Once construction finishes and the key is set, it returns the full artifact ref as intended

[nathanwilliams-ct]

LGTM