Add prepare and pretest lifecycle scripts to auto-build dist/

[Copilot]

With dist/ removed from the repo, npm test and Git-based installs fail because main/module/exports reference ./dist/* files that no longer exist without an explicit build step.

Changes

• prepare: triggers rollup -c after npm install, covering both local development and direct Git installs
• pretest: triggers rollup -c before npm test, ensuring dist/ is always present when examples run

"scripts": {
  "build": "rollup -c",
  "prepare": "npm run build",
  "prepublishOnly": "npm run build",
  "pretest": "npm run build",
  "test": "..."
}

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[Copilot]

Pull request overview

This PR ensures dist/ is generated automatically so installs/tests don’t fail now that built artifacts are no longer committed, aligning package entrypoints (main/module/exports) with the on-disk build output.

Changes:

• Add an npm prepare script to build dist/ after install (notably for Git-based installs).
• Add an npm pretest script to build dist/ before running example-based tests.

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[Copilot]

With prepare added, npm publish / npm pack will also run the build via prepare (npm lifecycle), so keeping prepublishOnly will typically run the build twice during publishing. Consider removing prepublishOnly (or prepare) to avoid redundant builds and potential non-deterministic artifact differences.

Suggested change

"prepublishOnly": "npm run build",