Copy constructor for result set and entity

Summary

These changes support a better handling of the ResultSet and Entity objects when their owners are to be deleted (e.g. in clients which delete transansaction due to end of the scope of a function while they return an entity or the resultset of said transaction)

These changes are needed for caosdb-julialib!12 (merged)

The server is just being updated for version-compatibility reasons: caosdb-server!31 (merged)

Focus

• Refactoring of the ResultSet and Entity class' copy constructors (amd a general clean-up of the Entity constructor)
• Additional Transaction::ReleaseResultSet and ResultSet::release_at methods which release the unique_ptr from their owning objects.

Test Environment

• CPP Integration tests in caosdb-cppinttest!15 (merged)
• Julia integration tests in

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• Reference related Issues
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  • 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
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include/caosdb/value.h

@@ -63,11 +63,9 @@ public:
     return (this->wrapped->scalar_value_case() == ScalarValueCase::kStringValue) ||
            (this->wrapped->scalar_value_case() == ScalarValueCase::kSpecialValue &&
             this->wrapped->special_value() == ProtoSpecialValue::SPECIAL_VALUE_EMPTY_STRING);
-    return false;
   }
   [[nodiscard]] inline auto AsString() const noexcept -> const std::string & {
     return this->wrapped->string_value();
-    ;
   }
 
   [[nodiscard]] inline auto IsDouble() const noexcept -> bool {