Test classic content scripts through actual-source VM evaluation

A classic non-module browser content script can be regression-tested against its actual shipped source without production-only exports: evaluate it in a Node VM with only the required browser globals stubbed, then call its top-level functions from the VM context.

Neutralize boot timers and observers explicitly. Assert pure normalization precedence and fallback behavior against the same function body shipped to the browser. Keep real-browser or unpacked-extension checks separate when DOM, isolation, permissions, or network behavior changes, because VM evaluation proves none of those boundaries.