test: add jest, configure path aliases, and add test step to CI workflow

Author: toasted323

.github/workflows/ci.yml

@@ -27,6 +27,9 @@ jobs:
       - name: Install dependencies
         run: npm ci
 
+      - name: Run tests
+        run: npm test
+
       - name: Build with Rollup
         run: npm run build
 

jest.config.js

@@ -0,0 +1,5 @@
+export default {
+  moduleNameMapper: {
+    "^\\$lib/(.*)$": "<rootDir>/src/lib/$1",
+  },
+};