refactor: rewrite Module as an ES6 class

[KristjanESPERANTO]

This PR rewrites module.js to use a native ES6 class instead of Class.extend() - the same old inheritance helper that was removed from node_helper.js in #4147.

The normal module API stays the same: modules still use Module.register({...}). Internally, Module.create() now creates a named subclass for each module, copies over a cloned definition, and only calls init() when it is actually a function.

Outcome: one less file in the browser bundle, no more magic _super() wiring, better stack traces, and tests for the module creation path that did not exist before. module.js is also now a plain class with no external dependencies - an intentional step towards export default Module when browser scripts eventually move to native ES modules.

Since these changes touch the core of how modules are created, I'd appreciate a close review and any feedback on edge cases I may have missed.

[khassel]

@KristjanESPERANTO let me know if you want to wait for other reviews, otherwise I will merge it ...

[KristjanESPERANTO]

@khassel I think one review is enough. Thanks! 🙂