Support service worker testing

Clear and concise description of the problem

Service workers are complicated, so having unit tests for them where you can inspect every caching decision can be important.

Currently I'm not familiar with any way to test in a service worker environment with vitest. It would be great if it supported that.

I had a quick go and I got a hard error:

Error: This module can only be imported inside a service worker

I will try look for a workaround, but generally it would be good to have decent support for the service worker use case

Suggested solution

Add service worker environment testing

Alternative

playwright? Though I'm not sure it has good support either + you can't inspect every decision to ensure caches are correctly added / removed in all scenarios

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Start by reproducing the reported import error in Vitest when testing a service worker environment. Review the existing environment-testing entry points and determine how service-worker execution and cache decisions should be inspected. Done means service-worker unit tests run without the environment error and the supported behavior is documented.