Start adding the Wuerstchen diffusion pipeline (#843)

* Wuerstchen common bits.

* Add the prior layer.

* Start adding diffnext.

candle-transformers/src/models/wuerstchen/diffnext.rs

@@ -0,0 +1,55 @@
+#![allow(unused)]
+use super::common::{GlobalResponseNorm, ResBlock, TimestepBlock, WLayerNorm};
+use candle::{DType, Module, Result, Tensor, D};
+use candle_nn::VarBuilder;
+
+#[derive(Debug)]
+pub struct ResBlockStageB {
+    depthwise: candle_nn::Conv2d,
+    norm: WLayerNorm,
+    channelwise_lin1: candle_nn::Linear,
+    channelwise_grn: GlobalResponseNorm,
+    channelwise_lin2: candle_nn::Linear,
+}
+
+impl ResBlockStageB {
+    pub fn new(c: usize, c_skip: usize, ksize: usize, vb: VarBuilder) -> Result<Self> {
+        let cfg = candle_nn::Conv2dConfig {
+            groups: c,
+            padding: ksize / 2,
+            ..Default::default()
+        };
+        let depthwise = candle_nn::conv2d(c, c, ksize, cfg, vb.pp("depthwise"))?;
+        let norm = WLayerNorm::new(c, vb.pp("norm"))?;
+        let channelwise_lin1 = candle_nn::linear(c + c_skip, c * 4, vb.pp("channelwise.0"))?;
+        let channelwise_grn = GlobalResponseNorm::new(4 * c, vb.pp("channelwise.2"))?;
+        let channelwise_lin2 = candle_nn::linear(c * 4, c, vb.pp("channelwise.4"))?;
+        Ok(Self {
+            depthwise,
+            norm,
+            channelwise_lin1,
+            channelwise_grn,
+            channelwise_lin2,
+        })
+    }
+
+    pub fn forward(&self, xs: &Tensor, x_skip: Option<&Tensor>) -> Result<Tensor> {
+        let x_res = xs;
+        let xs = xs.apply(&self.depthwise)?.apply(&self.norm)?;
+        let xs = match x_skip {
+            None => xs.clone(),
+            Some(x_skip) => Tensor::cat(&[&xs, x_skip], 1)?,
+        };
+        let xs = xs
+            .permute((0, 2, 3, 1))?
+            .apply(&self.channelwise_lin1)?
+            .gelu()?
+            .apply(&self.channelwise_grn)?
+            .apply(&self.channelwise_lin2)?
+            .permute((0, 3, 1, 2))?;
+        xs + x_res
+    }
+}
+
+#[derive(Debug)]
+pub struct WDiffNeXt {}