test(local-storage): add unit tests

tests/LocalStorage/LocalStoragePrimitive.test.svelte

@@ -0,0 +1,18 @@
+<script lang="ts">
+  import { LocalStorage } from "carbon-components-svelte";
+
+  const primitiveValue = "test-value";
+</script>
+
+<div data-testid="primitive-storage">
+  <LocalStorage
+    key="test-key"
+    value={primitiveValue}
+    on:save={() => {
+      console.log("save event");
+    }}
+    on:update={({ detail }) => {
+      console.log("update event", detail);
+    }}
+  />
+</div>