fix: mark package as side-effect free (#630)

[Tree shaking](https://webpack.js.org/guides/tree-shaking/) results in smaller web bundles by deleting unused code.

This module is side-effect free so mark it as such to signal to bundlers that unused exports can be excluded from bundles.

Author: achingbrain

package.json

@@ -208,5 +208,6 @@
   },
   "browser": {
     "dist/test/utils/create-libp2p-node.js": false
-  }
+  },
+  "sideEffects": false
 }