Universal Process Unload Handler

The `unload` package provides a unified API for executing code reliably when a JavaScript process or environment is about to exit or unload. It abstracts away environment-specific mechanisms like `process.on('beforeExit')`, `process.on('SIGINT')`, `process.on('uncaughtException')` in Node.js, and `window.addEventListener('beforeunload')` or `window.addEventListener('unload')` in browsers, Electron, React Native, workers, and iframes. This ensures the registered exit functions are called only once, regardless of how the environment terminates. The current stable version is 2.4.1. It is particularly useful for library authors who need to clean up resources consistently across diverse JavaScript runtimes, ensuring robust shutdown procedures. It differs from simply using `process.on('exit')` by also handling abnormal terminations like `SIGINT` and `uncaughtException` in Node.js, and browser tab/window closures.