Trail for further supression on noises

As it known to all, noises are common challenges under low-light scenes. After replication, I find that the noise level in your results are somehow too high. Have you tried some Total-Invariant (TV) Loss or other techniques during your experiences? In face, they are really easy to implement by adding an addition `certerion` in `diffusion_llie.py`.

Looking forward for your valuable reply~😉