paged-attention: build Torch 2.12 (#804)

* paged-attention: build Metal/CUDA for Torch 2.12

* Update flake

Author: danieldk

paged-attention/flake.lock

@@ -2,7 +2,7 @@
   description = "Flake for attention kernels";
 
   inputs = {
-    kernel-builder.url = "github:huggingface/kernels";
+    kernel-builder.url = "github:huggingface/kernels/torch-2.12";
   };
 
   outputs =