`vi.mock()` not working with `cloudflare:test` setup file imports

### What versions & operating system are you using?

System:
OS: macOS 15.5
CPU: (8) arm64 Apple M2
Memory: 178.98 MB / 24.00 GB
Shell: 4.0.2 - /opt/homebrew/bin/fish
Binaries:
Node: 22.17.1 - ~/.local/state/fnm_multishells/13811_1754254652214/bin/node
npm: 10.9.2 - ~/.local/state/fnm_multishells/13811_1754254652214/bin/npm
bun: 1.2.19 - ~/.bun/bin/bun
npmPackages:
@cloudflare/vitest-pool-workers: ^0.8.59 => 0.8.59

### Please provide a link to a minimal reproduction

https://github.com/jimmycallin/cloudflare-workers-d1-vitest-mock-issue

### Describe the Bug

When using Vitest with Cloudflare Workers and importing modules from cloudflare:test in a setup file, `vi.mock()`calls are not being applied.

I'm not entirely sure if this is a vitest or a wrangler issue, but I spent quite a few hours debugging this issue, so I thought I could at least post it here for sake of posterity.

Reproduction:

- Set up a vitest config with a setup file that imports from cloudflare:test (e.g., applyD1Migrations)
- Mock a module using `vi.mock()` in a test file
- Run tests - the mock won't be applied

Expected: Mocks should work regardless of setup file imports.

Actual: Mocks are ignored when setup file contains cloudflare:test imports.

Workaround: Call `vi.resetModules()` before setting up the mock.

### Please provide any relevant error logs

_No response_