feat: allow customizing the alpha and beta parameters of the beta scheduler

[wbruna]

Summary

Include alphaand beta as extra-sample-args parameters to customize the Beta scheduler. This allows replicating the beta57 scheduler from https://github.com/ClownsharkBatwing/RES4LYF , as well as approximating several other schedulers.

I'm not so sure about the parameter names, since alpha and beta could potentially collide with sampler parameters (euler_ge has a gamma already...).

Additional Information

A random example:

sd-cli --diffusion-model anima-base-v1.0.safetensors --llm Josiefied-Qwen3-0.6B-abliterated-v2.Q8_0.gguf -W 768 -H 1024 --vae Qwen2D_VAE.safetensors --lora-model-dir . --steps 10 --cfg-scale 1 -p '3d anime style, selfie, Jenny Everywhere, round aviation goggles, scarf, Native American, making a V gesture, in a Japanese garden lora:anima-turbo-lora-v0.1:1' --diffusion-fa --sampling-method euler --scheduler beta --extra-sample-args alpha=$ALPHA,beta=$BETA

alpha=0.6,beta=0.6	alpha=0.5,beta=0.7	alpha=2.0,beta=2.0

Checklist

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