Timeseries: Fix constructor for ca.DM and support float arguments
According to the typing hints, a ca.DM should have been supported, but it would fail with an Exception because it does not support len().
Furthermore, the code in the constructor seemed to suggest support for floats (and integers), due to the "np.full_like" branch. The typing hints did however not cover this, and neither did it work in practice because of the len() call.