test: check code with ESLint

`npm run lint:eslint` (run as part of `npm lint` and `npm test`) now
checks our code with ESLint.

This also fixes or disables all lint failures.

eslint.config.js

@@ -0,0 +1,31 @@
+import globals from 'globals'
+import pluginJs from '@eslint/js'
+import tseslint from 'typescript-eslint'
+
+export default [
+  { files: ['**/*.{js,mjs,cjs,ts}'] },
+  { languageOptions: { globals: globals.node } },
+  pluginJs.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    ignores: ['dist/', 'generated/', 'intermediate/'],
+  },
+  {
+    rules: {
+      '@typescript-eslint/ban-ts-comment': [
+        'error',
+        {
+          'ts-expect-error': false,
+        },
+      ],
+      '@typescript-eslint/no-explicit-any': 'off',
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          varsIgnorePattern: '^_',
+          argsIgnorePattern: '^_',
+        },
+      ],
+    },
+  },
+]