Dilated convolutions (#657)

* Add the dilation parameter.

* Restore the basic optimizer example.

* Dilation support in cudnn.

* Use the dilation parameter in the cpu backend.

* More dilation support.

* No support for dilation in transposed convolutions.

* Add dilation to a test.

* Remove a print.

* Helper function.

candle-examples/examples/yolo-v8/model.rs

@@ -93,6 +93,7 @@ impl ConvBlock {
             padding,
             stride,
             groups: 1,
+            dilation: 1,
         };
         let conv = conv2d_no_bias(c1, c2, k, cfg, vb.pp("conv"))?;
         let bn = batch_norm(c2, 1e-3, vb.pp("bn"))?;