CCCL cudax/test/execution/test_then.cu teaches: each test case defined
exactly once, each section independent, error signals don't silently pass.
verify_functional.py had 9 functions defined twice. Python silently
overwrites the first definition with the second. The second ALL_TESTS.extend
also added duplicate entries causing tests to run twice.
Removed the entire duplicate block. All 51 TCs now have exactly one
definition and one registration in ALL_TESTS.