Handles Volt test virtual imports.

The current runner exposes the volt:test API as globals inside the QuickBEAM runtime. This module removes imports from volt:test and volt:test/browser before normal Volt compilation so users can still write idiomatic test files:

import { test, expect } from "volt:test"

test("works", () => {
  expect(1 + 1).toBe(2)
})

The rewrite is AST-backed and only removes actual import declarations whose source literal is a Volt test virtual module.