ret_check error appearing in some tests

[DanPuzzuoli]

Examples of this error can be found the testing environment (search ret_check):

macos: https://github.com/qiskit-community/qiskit-dynamics/actions/runs/12932990377/job/36073389618
ubuntu: https://github.com/qiskit-community/qiskit-dynamics/actions/runs/12932990377/job/36073389110

I've posted a small example causing this error on my local machine as a JAX issue. This is a very basic example use case of JAX's odeint function, so it appears to be an issue with JAX itself. While the stack trace doesn't point to where it's happening, it does mention an issue of float v.s. complex, which is consistent with the changes described in the issue that cause the code to run properly.

[DanPuzzuoli]

PR #380 provides a temporary workaround to the test_jax_transformations.py file by adding 1e-16j to y0 in the tests. This forces JAX to recognize the complex dtype, bypassing the type checking error.

This should be removed when possible once the issue is fixed in JAX.