Upgrade and fix eslint config (#2879)

Previously, `npm install; npm run lint` would fail. Now it succeeds.

This involved a couple changes:
1. switch from eslint legacy to flat config
2. bump some plugins, including removing some straggling references to the unmaintained `eslint-plugin-node` in favor of its sucessor `eslint-plugin-n` and removing `eslint-plugin-import`, which is unused and incompatible with eslint 9.
3. Use the recommended config for `typescript-eslint`.
4. Turn off the rule `@typescript-eslint/no-require-imports`, which currently fails on parts of the codebase.

---------

Co-authored-by: Francis Gulotta <[email protected]>

Author: rotu

.eslintignore

@@ -0,0 +1,68 @@
+import nodePlugin from 'eslint-plugin-n'
+import mocha from 'eslint-plugin-mocha'
+import globals from 'globals'
+import js from '@eslint/js'
+import eslintConfigPrettier from 'eslint-config-prettier'
+import eslint from '@eslint/js'
+import typescriptEslint from 'typescript-eslint'
+
+export default [
+  {
+    ignores: ['packages/*/node_modules', '**/docs', 'packages/*/dist/*'],
+  },
+  js.configs.recommended,
+  nodePlugin.configs['flat/recommended-script'],
+  mocha.configs['flat'].recommended,
+  ...typescriptEslint.configs.recommended,
+  eslintConfigPrettier,
+  {
+    languageOptions: {
+      globals: {
+        ...globals.node,
+        ...globals.mocha,
+        assert: false,
+        makeTestFeature: false,
+        shouldReject: false,
+      },
+      ecmaVersion: 12,
+      sourceType: 'commonjs',
+    },
+
+    rules: {
+      'no-extra-semi': 'off',
+      '@typescript-eslint/no-extra-semi': 'off',
+      'n/no-process-exit': 'off',
+      'no-var': 'error',
+
+      'n/no-extraneous-import': [
+        'error',
+        {
+          allowModules: ['sinon', 'chai'],
+        },
+      ],
+
+      'n/no-missing-import': 'off',
+      'n/no-missing-require': 'off',
+      'n/no-unpublished-import': 'off',
+      'n/no-unpublished-require': 'off',
+      'n/no-unsupported-features/es-builtins': 'error',
+      'n/no-unsupported-features/es-syntax': 'off',
+      'n/no-unsupported-features/node-builtins': 'error',
+      'n/hashbang': 'off',
+      'object-shorthand': 'error',
+      'prefer-arrow-callback': 'error',
+      'prefer-const': 'error',
+      'prefer-template': 'error',
+      'mocha/no-exclusive-tests': 'error',
+      'mocha/no-hooks-for-single-case': 'off',
+      'mocha/no-mocha-arrows': 'off',
+      'mocha/no-pending-tests': 'error',
+      'mocha/no-setup-in-describe': 'off',
+      strict: ['error', 'never'],
+      'valid-jsdoc': 'off',
+      '@typescript-eslint/no-var-requires': 'off',
+      '@typescript-eslint/no-empty-function': 'off',
+      '@typescript-eslint/no-require-imports': 'off',
+    },
+  },
+]