Add Stable Diffusion 3 Example (#2558)

* Add stable diffusion 3 example

Add get_qkv_linear to handle different dimensionality in linears

Add stable diffusion 3 example

Add use_quant_conv and use_post_quant_conv for vae in stable diffusion

adapt existing AutoEncoderKLConfig to the change

add forward_until_encoder_layer to ClipTextTransformer

rename sd3 config to sd3_medium in mmdit; minor clean-up

Enable flash-attn for mmdit impl when the feature is enabled.

Add sd3 example codebase

add document

crediting references

pass the cargo fmt test

pass the clippy test

* fix typos

* expose cfg_scale and time_shift as options

* Replace the sample image with JPG version. Change image output format accordingly.

* make meaningful error messages

* remove the tail-end assignment in sd3_vae_vb_rename

* remove the CUDA requirement

* use default_value in clap args

* add use_flash_attn to turn on/off flash-attn for MMDiT at runtime

* resolve clippy errors and warnings

* use default_value_t

* Pin the web-sys dependency.

* Clippy fix.

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Co-authored-by: Laurent <laurent.mazare@gmail.com>

candle-transformers/src/models/mmdit/projections.rs

@@ -42,7 +42,6 @@ pub struct QkvOnlyAttnProjections {
 
 impl QkvOnlyAttnProjections {
     pub fn new(dim: usize, num_heads: usize, vb: nn::VarBuilder) -> Result<Self> {
-        // {'dim': 1536, 'num_heads': 24}
         let head_dim = dim / num_heads;
         let qkv = nn::linear(dim, dim * 3, vb.pp("qkv"))?;
         Ok(Self { qkv, head_dim })