fix: support manual overrides via context.route or page.route

[kettanaito]

Changes

• Use route.fallback() for unhandled routes so they can be tapped into route handlers defined by the user (via context.route or page.route in their tests).
• Add the missing test cases.

Somehow, this also significantly reduces the probability of #35. I don't see any reason that would happen, but it does. route.fallback() still has the _handledPromise check built in, but it seems to error quite less.

[kettanaito]

Released: v0.6.3 🎉

This has been released in v0.6.3.

• 📄 Release notes
• 📦 View on npm

Get these changes by running the following command:

npm i @msw/playwright@latest

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