feat!: add support for ESLint v9

Fixes #2

BREAKING CHANGE: peerDependencies:
`eslint@^9.12.0`
`eslint-plugin-promise@^7.1.0`
`eslint-plugin-unicorn@^56.0.0`
`globals@^15.10.0`
`typescript-eslint@^8.8.0`

BREAKING CHANGE: Node.js >= 20.9.0

test/basic.js

@@ -1,20 +0,0 @@
-const test = require("node:test")
-const assert = require("node:assert/strict")
-
-const config = require("../index.js")
-
-/**
- * @param {unknown} object
- * @returns {boolean}
- */
-const isObject = (object) => {
-  return typeof object === "object" && object !== null
-}
-
-test("test basic properties of config", async () => {
-  assert.ok(isObject(config))
-  assert.ok(isObject(config.parserOptions))
-  assert.ok(isObject(config.env))
-  assert.ok(isObject(config.rules))
-  assert.ok(isObject(config.overrides))
-})

test/validate-config.js

@@ -1,13 +1,9 @@
-const test = require("node:test")
-const assert = require("node:assert/strict")
+import test from "node:test"
+import assert from "node:assert/strict"
 
-const { ESLint } = require("eslint")
+import { ESLint } from "eslint"
 
-const eslint = new ESLint({
-  ignore: false,
-  useEslintrc: false,
-  overrideConfigFile: "eslintrc.json",
-})
+const eslint = new ESLint()
 
 test("ensure we validate correctly JavaScript files", async () => {
   const [noErrors] = await eslint.lintFiles(