Major overhaul / better native integration

[city96]

The plan is to do a full rewrite/refactor of this repo to have better integration with most of the native comfy code.
This should make things less fragile (and less cumbersome in general).

Progress/steps:

• Remove HyDiT (already supported in base ComfyUI)
• Rewrite PixArt base code
• Add T5 for PixArt
• Rewrite Sana base code
• Add Gemma for Sana [mostly done, missing logic]
• Rewrite DiT base code
• Rewrite VAE loader
• Add back LoRA support

Major changes:

• Text encoders return comfy compatible CLIP objects instead of custom types
• Auto config detection wherever possible to minimize user error
• Single node with dropdown for all models instead of separate node sets per model
• PixArt/DiT/etc models are loaded from unet (diffusion_models) folder instead of checkpoints folder

Other possible ideas/plans:

• GGUF support if ComfyUI-GGUF is installed
• Generic resolution select node with dropdown and slider/float input
• Change to native comfy attention for PixArt/Sana
• Add proper ControlNet for PixArt (current version never worked correctly)