Fix mistral attention on Metal (#2699)

Co-authored-by: Luka Zakrajsek <luka.zakrajsek@soniox.com>

candle-transformers/src/models/mistral.rs

@@ -262,7 +262,8 @@ impl Attention {
             .contiguous()?;
         let value_states = value_states
             .reshape((b_sz, q_len, self.num_kv_heads, self.head_dim))?
-            .transpose(1, 2)?;
+            .transpose(1, 2)?
+            .contiguous()?;
 
         let (query_states, key_states) =
             self.rotary_emb