Adding tree-shaking test

[peripateticus]

Description

In #131, Cedar was updated to be tree-shakeable, this PR follows up on that and adds unit test to ensure tree-shaking is working as expected.

What this test does:

• builds Cedar,
• builds an app that imports CdrButton from dist/lib.mjs ,
• verifies that only CdrButton is in the app bundle.

Implementation notes:

• In the test, I’m re-building Cedar rather than requiring that a build happen prior to running the unit tests. Test can run independently of a build. This results in a longer running test so I had to bump the test timeout.
• I’m building to a separate dist directory, /dist-test and import from that in the test app so that we aren’t overwriting Cedar’s default /dist directory.
• I’m exporting the raw config object from vite.config.mjs because I need to update values prior to the defineConfig call, then I call defineConfig within the test.

Checklist:

Design:

• Reviewed with designer and meets expectations

Cross-browser testing:

• Chrome
• Firefox
• Edge
• Safari
• iOS
• Android

Unit testing:

• Sufficient unit test coverage (see unit test best practices for ideas)
• Snapshot updates are explained with comment and reference the relevant source code change

A11y:

• Meets WCAG AA standards

Documentation:

• API docs created/updated
• Examples created/updated