Fix slice offset semantics in mockState.ts

The createMockState adapter used a right-aligned big-endian
calculation (32 - offset - length) for stack, storage, and
transient slice offsets. The correct convention is direct
byte offset from the start of the word, matching the
ganache test adapter and evm machine adapter.

Author: gnidan

packages/pointers-react/src/utils/mockState.ts

@@ -79,9 +79,9 @@ export function createMockState(spec: MockStateSpec): Machine.State {
         return entry;
       }
       const { offset, length } = slice;
-      const startByte = 32 - Number(offset) - Number(length);
-      const endByte = startByte + Number(length);
-      return Data.fromBytes(entry.slice(startByte, endByte));
+      return Data.fromBytes(
+        entry.slice(Number(offset), Number(offset + length)),
+      );
     },
   };
 
@@ -115,9 +115,9 @@ export function createMockState(spec: MockStateSpec): Machine.State {
         return value;
       }
       const { offset, length } = slice;
-      const startByte = 32 - Number(offset) - Number(length);
-      const endByte = startByte + Number(length);
-      return Data.fromBytes(value.slice(startByte, endByte));
+      return Data.fromBytes(
+        value.slice(Number(offset), Number(offset + length)),
+      );
     },
   };
 
@@ -190,9 +190,9 @@ export function createMockState(spec: MockStateSpec): Machine.State {
         return value;
       }
       const { offset, length } = slice;
-      const startByte = 32 - Number(offset) - Number(length);
-      const endByte = startByte + Number(length);
-      return Data.fromBytes(value.slice(startByte, endByte));
+      return Data.fromBytes(
+        value.slice(Number(offset), Number(offset + length)),
+      );
     },
   };