As discussed in #10357, ember-cli-mirage isn't particularly well maintained anymore and blocking a couple of dependency updates.

This PR migrates us from using ember-cli-mirage for the mock API in the frontend test suites towards using msw and @mswjs/data.

I've used a pnpm workspace to add a subpackage at packages/crates-io-msw, that is roughly equivalent to the previous top-level mirage folder. This package contains:

• all of the msw request handlers to simulate our crates.io API (exported as handlers)
• the @mswjs/data database with all of the models that support the above request handlers (exported as db)
• the data from mirage/fixtures/ and a loadFixtures() function

The package also contains its own dedicated test suite. The test suite is essentially a vitest port of the previous tests/mirage/ tests, but running in Node.js to simplify their development.

The @crates-io/msw package is integrated into the QUnit test suite by a setupMsw() function (similar to the previous setupMirage()). This function sets up the mock service worker and database for each test and ensures proper cleanup of both after the test has finished.

The package is also integrated into the Playwright test suite (at e2e/). Here, it is using a msw fixture, that can be used in tests and sets up playwright-msw which transforms the msw request handlers into Playwright request handlers. The msw fixture has three properties, worker is controlling the HTTP mocking, db is the @mswjs/data database mentioned above, and authenticateAs() is roughly equivalent to the similarly-named function from before. Since the mocking is now running on the Playwright side instead of inside the browser the test code could be simplified significantly.

I'm aware that the diff is big, and I'm happy to split it up into more manageable chunks if it helps. I definitely recommend reviewing in "ignore whitespace changes" mode. I've tried to group the commits thematically so that the can be reviewed in smaller chunks too. Let me know if/how I can help in getting this reviewed! :)

Closes #10357

Related:

• Replace ember-cli-mirage with direct miragejs usage #10357