Fix loading diffusers model (+support F64/I64 types)

[stduhpf]

Loading diffusers models wasn't working, this fixes it for me,. I also added support for SDXL diffusers model (the second text encoder wasn't being handled).

During testing, I came across models with 64bit types, so I added support for those too since they are supported by GGML. (Fixes #153, #669)

[stduhpf]

It would be nice to get it to work for DiT models too, but it looks like a lot of work, because qkv matrices are split in diffusers format. That would probably require a significant refactor of the model loading logic...
Maybe just refactoring the model-specific code itself to accomodate for the different convetions could be a potential solution too

[stduhpf]

This is breaking some LoRAs.

[leejet]

Thank you for your contribution.

[wbruna]

@stduhpf , I'm getting an 'f64 unsupported' error trying the model mentioned on #153 ( https://civitai.com/models/7371/rev-animated?modelVersionId=425083 , fp32 file):

./sd --model ./revAnimated_v2Rebirth.safetensors -p flower 
ggml_vulkan: Found 1 Vulkan devices:
ggml_vulkan: 0 = AMD Radeon RX 7600 XT (RADV NAVI33) (radv) | uma: 0 | fp16: 1 | warp size: 64 | shared memory: 65536 | int dot: 1 | matrix cores: KHR_coopmat
[INFO ] stable-diffusion.cpp:210  - loading model from './revAnimated_v2Rebirth.safetensors'
[INFO ] model.cpp:998  - load ./revAnimated_v2Rebirth.safetensors using safetensors format
[INFO ] stable-diffusion.cpp:259  - Version: SD 1.x 
[INFO ] stable-diffusion.cpp:292  - Weight type:                 f32
[INFO ] stable-diffusion.cpp:293  - Conditioner weight type:     f32
[INFO ] stable-diffusion.cpp:294  - Diffusion model weight type: f32
[INFO ] stable-diffusion.cpp:295  - VAE weight type:             f16
  |====================>                             | 459/1130 - 0.00it/sterminate called after throwing an instance of 'std::runtime_error'
  what():  type f64 unsupported for integer quantization: no dequantization available
Abortado (imagem do núcleo gravada)

This is on master-dafc32d .

[stduhpf]

Yeah, F64 is still not properly supported. I didn't realize there isn't a built in "dequantization" (or rather quantization in that case) function for F64 to F32 in GGML, so I just implemented it with #726. This fix the crash during loading time, but I can't get inference to run with either Vulkan or CPU backends when using the models with F64 weights. Forcing it to use F32 works with the new new changes I made ( --type f32).