fix(): Handle numpy arrays in Expression.dimensions property

[benflexcompute]

fix: Handle numpy arrays in Expression.dimensions property

Fixed AssertionError when setting output_units on expressions that evaluate
to plain numpy arrays (e.g., math.exp(solution.CfVec[0])). Changed the
dimensions property to explicitly handle numpy.ndarray types as dimensionless
instead of using assertion.

Added regression test to prevent future issues.

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Note

Fixes Expression.dimensions to treat plain numbers and numpy.ndarray results as dimensionless and to raise a clear error for unsupported types. Adds a regression test ensuring math functions returning numpy arrays (e.g., math.exp(solution.CfVec[0])) are handled and that setting output_units remains valid.

• Update types.py: adjust Expression.dimensions logic (dimensionless for Number/np.ndarray; remove assert; add explicit ValueError for unknown types)
• Add tests/simulation/test_expressions.py: new test test_dimensions_with_numpy_array_result covering solver variable, math function, plain numbers, and output_units assignment

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