add a parameter for the number of highres iterations

[ssube]

The highres feature, which is the equivalent of the highres fix for auto1111, can be run repeatedly to increase the image size exponentially without really increasing the amount of VRAM required.

Add a parameter to the client and server, allowing users to run highres more than once. For example, a 512 image with 2x upscaling and 3 rounds of highres will produce a final output of 4k, with 8x8 tiles in the final iteration. This helps to reduce the seams between tiles.