Chart Library: Add initial testing infrastructure and PieChart component tests

[annacmc]

Proposed changes:

Sets up the initial testing infrastructure for the charts package, including Jest configuration, test environment setup, and initial test cases for the PieChart component. This PR focuses solely on the testing setup, with component behavior fixes and additional tests to follow in subsequent PRs.

cc: @jeherve - have I taken the best approach here? any dependencies I don't actually need (or am missing?) also checking the dir structure first with Jetpack style in keeping the tests close to the components.

Additionally, can I merge with failing tests, as the purpose of this is to highlight what needs to be worked on and fixed up - with the intention of follow up PRs addressing the failing tests. I'm not sure if GH will let me merge this way or not as Tests / JS tests (pull_request) is required.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

1. Run tests for the charts package:

cd projects/js-packages/charts
pnpm test

2. Verify that tests run successfully (note: some test failures are expected in this PR and will be addressed in follow-up PRs)

This PR sets up the initial testing infrastructure for the charts package. Test failures are intentionally included.

[github-actions]

Are you an Automattician? The PR will need to be tested on WordPress.com. This comment will be updated with testing instructions as soon the build is complete.

[github-actions]

Thank you for your PR!

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