F fix merge entity conflicts

Summary

Part of https://gitlab.indiscale.com/caosdb/customers/leibniz-zmt/management/-/issues/125. Adds a new apiutils.empty_diff function to check for the identity of two Entity objects in the sense of no differences between the two entities. It also adds optional arguments to compare_entities and merge_entities to determine whether or not referenced Entity objects will be compared/merged.

Focus

Mainly, new cases to the value comparison of reference properties have been added to the compare_entities function. Note that the compare_referenced_records argument of the compare_entities function defaults False in order to restore the previous behavior. In contrast, the default of merge_references_with_empty_diffs of merge_entities is True because a) the function is Experimental anyway, so breaking previous behavior is ok, and b) in most of the (e.g., crawler) cases this is probably what a merge is expected to do.

Test Environment

Unit tests should be sufficient; but you can also test it with ZMT's Pangaea crawler.

Check List for the Author

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• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
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  • Intent of new code
  • Problems with old code
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Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
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src/caosdb/apiutils.py

@@ -269,7+269,7 @@
             olddiff["properties"][prop.name] = {}
 
             if (old_entity.get_importance(prop.name) !=
                     new_entity.get_importance(prop.name)):
                 olddiff["properties"][prop.name]["importance"] = \
                     old_entity.get_importance(prop.name)
                 newdiff["properties"][prop.name]["importance"] = \
@@ -297,7+297,7 @@
                     # list of references
                     elif isinstance(prop.value, list) and isinstance(matching[0].value, list):
                         # all elements in both lists actually are entity objects
+                        # TODO: check, whether mixed cases can be allowed or should lead to an error
                         if all([isinstance(x, Entity) for x in prop.value]) and all([isinstance(x, Entity) for x in matching[0].value]):
                             # can't be the same if the lengths are different
                             if len(prop.value) == len(matching[0].value):