Make tests compatible with SciPy 1.16

[edoaltamura]

Summary

Updates the argument definitions for the optimisers to match those in SciPy 1.16, similarly to qiskit-community/qiskit-algorithms#234

Fixes #957

[edoaltamura]

Now the .ravel() imposes gradients (jac) passed to optimisers like SLSQP to be strictly 1D arrays, required for compatibility with SciPy ≥1.16. Previously, we only wrapped gradients for the l-bfgs-b method and sometimes returned lists or higher-dimensional arrays, leading to errors. The fix generalises gradient wrapping for all methods and updates _wrap_gradient to always return a flattened 1D NumPy array via .ravel(), ensuring consistent behaviour across optimisers. This resolves test failures, and remains fully backwards-compatible with earlier SciPy versions.

[coveralls]

Pull Request Test Coverage Report for Build 17434461518

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 90.597%

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Totals
Change from base Build 17430028152:	0.04%
Covered Lines:	4625
Relevant Lines:	5105

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💛 - Coveralls