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-core/src/cudnn.rs

@@ -48,7 +48,7 @@ pub(crate) fn launch_conv2d<
     let conv = cudnn.create_conv2d::<T>(
         /* pad */ [params.padding as i32, params.padding as i32],
         /* stride */ [params.stride as i32, params.stride as i32],
-        /* dilation */ [1, 1],
+        /* dilation */ [params.dilation as i32, params.dilation as i32],
         cudarc::cudnn::sys::cudnnConvolutionMode_t::CUDNN_CROSS_CORRELATION,
     )?;
     let x_shape = [