Add narrow op dispatch to ComputeGraphExecutor

  The executor was missing a case for the narrow operation, causing
  graph execution to fail when MultiHeadAttention traces GQA head
  expansion (repeatKVHeads) into the optimized compute graph.

Author: michalharakal

skainet-compile/skainet-compile-dag/src/commonMain/kotlin/sk/ainet/lang/graph/exec/ComputeGraphExecutor.kt

@@ -195,6 +195,12 @@ public class ComputeGraphExecutor(
                 val dim = (params["dim"] as? Number)?.toInt() ?: 0
                 listOf(ops.unsqueeze(inputs[0], dim))
             }
+            "narrow" -> {
+                val dim = (params["dim"] as? Number)?.toInt() ?: 0
+                val start = (params["start"] as? Number)?.toInt() ?: 0
+                val length = (params["length"] as? Number)?.toInt() ?: 1
+                listOf(ops.narrow(inputs[0], dim, start, length))
+            }
 
             // Reduction ops
             "mean" -> {