Add sideEffects: false to all library packages

Enables tree-shaking for bundlers by marking all library packages
as side-effect-free.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/testing/virtual-authenticator/package.json

@@ -3,6 +3,7 @@
   "version": "0.0.1",
   "private": true,
   "type": "module",
+  "sideEffects": false,
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",
   "exports": {