Improving the compare_entities functions

Summary

I reviewed the compare_entities function from apiutils and identified some problematic cases (e.g. multi-properties). Corresponding unit tests have been created and the functionality repaired.

This is a preparation for a comprehensive review of the merge_entities function. I think it's a good idea to merge this in a first step as it's probably independent from the review of the merge function.

Focus

This one can probably be reviewed line-by-line. Maybe look for missing test-corner-cases that might be needed. The code for checking the value for equality is still not ideal, but I think a more comprehensive review (also adding the recursive reference checker) should be postponed.

Test Environment

There are unit tests.

Check List for the Author

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• All automated tests pass
• Reference related issues
• Up-to-date CHANGELOG.md (or not necessary)
• Up-to-date JSON schema (or not necessary)
• Appropriate user and developer documentation (or not necessary)
  • How do I use the software? Assume "stupid" users.
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• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md (or not necessary)
• Appropriate user and developer documentation (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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CHANGELOG.md

@@ -14,9 +14,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed ###
 
-- Improved `compare_entities` function, especially for unsuppored mulit-properties.
-  Updated the documentation and added more unit tests.
-
 ### Deprecated ###
 
 - getOriginUrlIn, getDiffIn, getBranchIn, getCommitIn (formerly apiutils) have been
@@ -25,7 +22,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Removed ###
 
 ### Fixed ###
+
 - Fixed `src/caosdb/utils/checkFileSystemConsistency.py`
+- `compare_entities` now corretly raises a `NotImplementedError` in case of
+  comparing two `Property` entities or in case of entities with multi
+  properties.
 
 ### Security ###