Prevent fallback to numpy in the test cases for `numexpr` execution

We use `numexpr` to accelerate execution and test it in `test_numexpr_execute.py`, however, it will fallback to `numpy` when encounters unsupported operands, we should avoid this kind of fallback in tests to ensure that all supported operands are executed by `numexpr` rather than fallback to `numpy`.

Start by reading test_numexpr_execute.py and trace how the tests invoke numexpr execution and permit fallback to numpy. Update the tests so supported operands are verified as running through numexpr rather than silently falling back, then run the relevant test file to confirm the fallback is detected.

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