WatNetv2

An improved version of the WatNet. Specifically,

1. The WatNetv2 is not applicable for Sentinel-2 image but also applicable for the Landsat series (Landsat-5, 7, 8 and 9) image.
2. The WatNetv2 achieved high surface water mapping accuracy by compared with WatNet.

Top accuracy: miou: 92.8%, oa: 95.6%, Unet, 20260215 deeplabv3plus_mb2, 92.3%, 20260216

To do: