chore: add linter setup (#57)

.eslintignore

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+node_modules
+out

.eslintrc.js

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+module.exports = {
+  root: true,
+  parser: '@typescript-eslint/parser',
+  plugins: ['@typescript-eslint', 'prettier'],
+  extends: ['eslint:recommended', 'plugin:@typescript-eslint/recommended'],
+  rules: {
+    'comma-spacing': ['error', { before: false, after: true }],
+    'no-unused-vars': 'off',
+    '@typescript-eslint/no-unused-vars': [
+      'warn', // or "error"
+      {
+        argsIgnorePattern: '^_',
+        varsIgnorePattern: '^_',
+        caughtErrorsIgnorePattern: '^_',
+      },
+    ],
+    'prettier/prettier': 'error',
+  },
+};

.github/workflows/formatting.yml

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+name: Formatting
+
+on:
+  pull_request:
+  merge_group:
+  push:
+    branches:
+      - master
+
+# This will cancel previous runs when a branch or PR is updated
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  eslint:
+    name: eslint
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 18.17.1
+          cache: 'npm'
+          cache-dependency-path: 'package-lock.json'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Run `npm run lint`
+        run: npm run lint

.prettierrc

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+{
+  "parser": "typescript",
+  "printWidth": 120,
+  "singleQuote": true,
+  "trailingComma": "all"
+}