Support mixed real/imaginary parameters with QGTJacobianDense

Created by: PhilipVinc

Before this PR, the matmul and solve interface of QGTJacobianDense is not consistent with the order of tree_to_Real and tree_ravel used by nk.jax.jacobian leading to wrong results if the pytree is non homogeneous (and maybe in other cases).

This PR fixes those inconsistencies, and now QGTJacobianDense can support pytrees with both real and complex parameters of the same (32/64) bit precision.