Refactor and parametrize Fourier Coefficients tests

Deleted test_fourier_coefficients_discrete.py and replaced its coverage by refactoring test_fourier_coefficients_pytest.py. The new test uses pytest parameterization to run the Fourier Coefficient workflow for each synthetic MTH5 file, improving maintainability and enabling parallel execution. All validation and workflow steps are now consolidated in a single, parameterized test.

Author: kujaku11