ci: add knip configuration

Author: davidabou

knip.json

@@ -0,0 +1,9 @@
+{
+  "$schema": "https://unpkg.com/knip@5/schema.json",
+  "workspaces": {
+    ".": {
+      "entry": ["src/index.ts"],
+      "ignore": ["playground/**"]
+    }
+  }
+}