Handle duplicate key

This merge request implements handling of JSON file with duplicated keys.

The consequence is that the system stops early rather than run with unexpected values.

Related to beat.core!69

Fixes #25 (closed)

beat/backend/python/test/prefix/algorithms/autonomous/invalid_loop_output/1.json

 {
-    "schema_version": 2,
+    "schema_version": 3,
     "language": "python",
     "api_version": 2,
     "type": "loop",