fix(core): Ensure correct ArrayBuffer return, fix fetch body typing, reorganize node-only tests, and bump tsbuild devDependency

ts/core_node/response.ts

@@ -115,10 +115,12 @@ export class CoreResponse<T = any>
    */
   async arrayBuffer(): Promise<ArrayBuffer> {
     const buffer = await this.collectBody();
-    return buffer.buffer.slice(
+    const sliced = buffer.buffer.slice(
       buffer.byteOffset,
       buffer.byteOffset + buffer.byteLength,
     );
+    // Ensure we return ArrayBuffer, not SharedArrayBuffer
+    return sliced instanceof ArrayBuffer ? sliced : new ArrayBuffer(0);
   }
 
   /**