Add error checker for duplicate codesystem codes

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.45%. Comparing base (497b9f2) to head (f420b69). Report is 99 commits behind head on master.

:exclamation: Current head f420b69 differs from pull request most recent head 2ba4fec

Please upload reports for the commit 2ba4fec to get more accurate results.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #6014 +/- ## ============================================ + Coverage 83.39% 83.45% +0.06% - Complexity 26927 27239 +312 ============================================ Files 1681 1697 +16 Lines 103965 105331 +1366 Branches 13189 13313 +124 ============================================ + Hits 86702 87908 +1206 - Misses 11613 11722 +109 - Partials 5650 5701 +51 ```

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