Fix casadi casadi conversion to array after Numpy 2.4 release

[Giulero]

This PR fixes the failing action https://github.com/gbionics/adam/actions/runs/20404127584 which fails the test idyntree_conversion with

/opt/hostedtoolcache/Python/3.11.14/x64/lib/python3.11/site-packages/adam/model/conversions/idyntree.py:23: in _to_sequence
    val = [float(v) for v in cs.DM(val).full()]
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

.0 = <iterator object at 0x7f11ce7734c0>

>   val = [float(v) for v in cs.DM(val).full()]
           ^^^^^^^^
E   TypeError: only 0-dimensional arrays can be converted to Python scalars

I guess after the release https://numpy.org/news/#numpy-240-released

Indeed there was a deprecation warning before the release:

tests/test_idyntree_conversion.py: 6750 warnings
adam/src/adam/model/conversions/idyntree.py:23: DeprecationWarning: Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future. Ensure you extract a single element from your array before performing this operation. (Deprecated NumPy 1.25.)
    val = [float(v) for v in cs.DM(val).full()]

tests/test_idyntree_conversion.py: 249 warnings
adam/src/adam/model/conversions/idyntree.py:42: DeprecationWarning: Conversion of an array with ndim > 0 to a scalar is deprecated, and will error in future. Ensure you extract a single element from your array before performing this operation. (Deprecated NumPy 1.25.)
    return float(val)

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📚 Documentation preview 📚: https://adam-docs--147.org.readthedocs.build/en/147/

[Copilot]

Pull request overview

This PR fixes a compatibility issue with NumPy 2.4 that caused test failures in the idyntree_conversion module. The problem arose from deprecated NumPy behavior that converted multi-dimensional arrays to scalars, which now raises a TypeError.

Key changes:

• Updated _to_sequence to properly flatten CasADi arrays using nested list comprehension
• Modified _to_scalar to extract scalar values from 2D arrays before conversion to float

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[Giulero]

Thanks @traversaro ! Merging.