test: cover userscript metadata contracts

[AlexTzib]

Hi @Manuito83, this is the test-only follow-up from the userscript DX work in #289.

The app already has the important pieces here, so this PR just adds focused coverage around the contracts we want to keep stable:

• @grant and @require parsing order
• preserving grants/requires through model creation and JSON round-trips
• replacing ###PDA-APIKEY### before injection
• preserving the existing smart quote normalization in adapted source

No runtime behavior is changed here. The goal is to make future userscript compatibility changes easier to review with less guesswork.

[Manuito83]

Thanks!