`bures_dist` return Nan

### Bug Description `bures_dist` can return Nan when computing the distance between the the same object. ### Code to Reproduce the Bug ```shell import qutip as qt dm = qt.rand_dm(3, seed=465) qt.bures_dist(dm, dm) ``` ### Code Output ```shell np.float64(nan) ``` ### Expected Behaviour Should return `0`. ### Your Environment ```shell Development version. ``` ### Additional Context _No response_