Convert to vitest

[TylerJDev]

No description provided.

[Copilot]

Pull Request Overview

This PR converts the test suite from Karma/Mocha to Vitest, modernizing the testing infrastructure for better developer experience and faster test execution.

Key changes:

• Replaced Karma/Mocha test runner with Vitest
• Updated test assertions from assert to expect syntax
• Modernized Node.js version to 18 in CI workflows

Reviewed Changes

Copilot reviewed 8 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
vitest.config.ts	New Vitest configuration with happy-dom environment and global test functions
test/setup.ts	Test setup file with polyfills and custom element registration for Vitest
test/attachment.test.ts	Converted test file from Mocha/assert to Vitest/expect syntax
test/.eslintrc.json	Removed Mocha-specific ESLint configuration
package.json	Updated scripts and dependencies to use Vitest instead of Karma
.github/workflows/publish.yml	Updated Node.js version from 14 to 18
.github/workflows/nodejs.yml	Updated Node.js version and workflow structure
.eslintignore	Added test setup file to ignore list

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[Copilot]

Using @ts-ignore suppresses TypeScript errors without explanation. Consider using @ts-expect-error with a comment explaining why this is necessary, or properly type the global declaration.

Suggested change

// @ts-ignore