fix: drop .js extensions from remaining relative imports

Extends 8111639 to cover __factories__, __seeds__, __contracts__, and
core-testing barrels.

packages/core-testing/src/react/index.ts

@@ -1,2 +1,5 @@
-export { renderWithProviders, type RenderOptions } from "./render-with-providers.js";
-export { createMockTrpcClient } from "./mock-trpc.js";
+export {
+  renderWithProviders,
+  type RenderOptions,
+} from "./render-with-providers";
+export { createMockTrpcClient } from "./mock-trpc";