extract createSetupTest for reusable test setup

[jycouet]

Moves the ~115-line setupTest boilerplate from the internal test suite into sv/testing as a createSetupTest(vitest) factory.

Internal tests now consume it the same way community add-ons will — a 3-line suite.ts.

Prep for community add-on improvements.

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Internal stuff

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Latest commit: b24d394

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commit: b24d394