feat!: update config for vitest and add package linters

[justlevine]

This pull request updates the JavaScript testing and linting workflows

Key changes:

• Renamed the reusable workflow from reusable-jest.yml to reusable-js-test.yml, making it runner-agnostic and updating all references and documentation accordingly. The workflow now runs JS unit tests via npm run test:js, allowing projects to choose their own test runner (e.g., Jest, Vitest, or others).

• Added a new lint script to package.json and updated the CI workflow to run npm run lint, ensuring both JS and JSON files are linted. [1] [2]

• Updated .lintstagedrc.mjs to use Prettier and ESLint for relevant file types, improving pre-commit formatting and linting.

• Removed the Jest ESLint plugin and configuration, replacing it with support for Vitest and a more flexible test file glob pattern.

• Added a top-level eslint.config.mjs that lints .mjs files and JSON using @eslint/json, and ensures the repo "dogfoods" its own shared config.