Bump to core-3.0.0, move to vitest, support ESM modules (#587)

__mocks__/fs.ts

@@ -0,0 +1,8 @@
+import { vi } from "vitest"
+
+export const createReadStream = vi.fn()
+export const statSync = vi.fn()
+export const readFileSync = vi.fn()
+export const writeFileSync = vi.fn()
+export const existsSync = vi.fn()
+export const realpathSync = vi.fn()