feat: swap / useFake

[Julien-R44]

Quick QOL helper. Adds a swap method on japa's TestContext that lets you replace a container binding with a fake for the duration of a test. binding gets auto-restored after the test completes via cleanup.

// via test ctx
test('sends welcome email', async ({ swap }) => {
  const fakeMailer = new FakeMailer()
  swap(Mailer, fakeMailer)

  await userService.register({ email: 'joe@example.com' })
  fakeMailer.assertSent('joe@example.com')
})

// via useFake
import { useFake } from '@japa/plugin-adonisjs/helpers'

test('sends welcome email', async () => {
  useFake(Mailer, new FakeMailer())

  await userService.register({ email: 'joe@example.com' })
  fakeMailer.assertSent('joe@example.com')
})

So i've been copy/pasting a little useFake helper across all my projects for a while now

it's pretty elegant compared to manually doing container.swap + container.restore in every single test, you just call it and forget about cleanup. felt like it deserved to live in the core properly instead of being a personal snippet