Add vitest (#123)

Add vitest example test and add GitHub action to run it.

Relatedly, add `.prettierrc` and a GitHub Action to check TypeScript
types.

.github/workflows/lint.yml

@@ -0,0 +1,24 @@
+name: Lint
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      # setup
+      - uses: actions/checkout@v4
+      - uses: oven-sh/setup-bun@v2
+
+      - name: Install package dependencies
+        run: bun install
+
+      # goal
+      - name: Check TypeScript types
+        run: bun run check
+
+      - name: Check code formatting
+        run: bun run format

.github/workflows/test.yml

@@ -0,0 +1,21 @@
+name: Test
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      # setup
+      - uses: actions/checkout@v4
+      - uses: oven-sh/setup-bun@v2
+
+      - name: Install package dependencies
+        run: bun install
+
+      # goal
+      - name: Run tests
+        run: bun run test

.prettierrc

@@ -0,0 +1,3 @@
+{
+  "singleQuote": true
+}

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+  "editor.defaultFormatter": "esbenp.prettier-vscode"
+}