add unit tests

this adds the groundwork to start unit testing some modules

src/vitest.config.ts

@@ -0,0 +1,18 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    projects: [
+      {
+        test: {
+          name: 'unit',
+          include: ['test/unit/*.{test,spec}.ts'],
+          environment: 'node',
+        },
+      },
+    ],
+    coverage: {
+      enabled: true,
+    },
+  },
+});