Add SA-Solver Sampler

[chaObserv]

Add SA-Solver by applying modifications of Comfy's UniPC whose source code is also based on DPM-Solver.

SA-Solver could be considered as a stochastic version UniPC with same order. When set eta = 0 constantly, its result is similar to UniPC (bh1).

The default tau function is adapted from official's repos and uses sigma percent to define interval.

Example (with --fp8_e5m2-unet):

[chaObserv]

I would convert this to a simplified version.

[chaObserv]

Extract sample functions and simplified the process, which makes it fit into k_diffusion. Instead of passing percent to sample function, SamplerSASolver node requires a model now to compute interval of tau function.

Landscape example:

Anime-style example: