feat(ssr-client-utils): add comprehensive tests for lwc-style component

[thedhanawada]

Summary

Adds comprehensive tests for the lwc-style component in @lwc/ssr-client-utils package.

Resolves #5272

Test Coverage

• Registration of lwc-style custom element
• Error handling for missing style-id and missing style elements
• First encounter behavior (stylesheet creation and caching)
• Cache reuse behavior with placeholder element creation
• Class preservation for hydration compatibility
• Karma test environment integration

Verification

• All 11 tests passing
• Build successful
• Linting passed
• Added package to vitest workspace configuration

[salesforce-cla]

Thanks for the contribution! Before we can merge this, we need @thedhanawada to sign the Salesforce Inc. Contributor License Agreement.

[thedhanawada]

CLA signed

[wjhsf]

Thanks for the contribution, @thedhanawada! However, this approach does not actually test the things that we need to validate. Rather than mocking every single interface, we need to run in a real browser (i.e. create Karma tests). The tests should validate that when an lwc-style is used, the component gets removed from the page, and that every component that uses an lwc-style inherits the correct styling, while those that do not use the component are unmodified.