feat: add easycache support

[rmatif]

This PR adds support for Easycache, a variant of TeaCache that achieves significant speedup

Currently tested only with CUDA and on Flux/Qwen

Command usage:

--easycache threshold,start_percent,end_percent

Examples:

Without Easycache	--easycache 0.2,0.15,0.95	Speedup
		x1.85
		x1.85

[Green-Sky]

Ran it with a SPARK (preview) Chroma finetune

thresh	img	real speedup
0		baseline
0.025		1.12x
0.1		1.31x
0.2		1.4x

I noticed the estimated speedup is off. It is off exactly by 2x, so I guess cfg is not handled properly yet.

eg. 40steps with cfg are actually 80 steps

40/(40-8) -> 1.25 (estimated 1.25)
80/(80-8) -> 1.11 (measured 1.12)

I included 0.025, because that is what the original used for wan.

Anyway Good stuff, I take the 11% speedup.