Full Playwright test integration

[steinybot]

Fixes #165 with true Playwright integration.

I only just saw this comment #173 (comment) on the previous PR (which I forgot to close). I had actually given up on that one a while ago as it was fraught with issues. It was never going to be true Playwright integration. It didn't actually fix #165 since it couldn't take screenshots.

I've been working on this version for quite a while as it was tough to get the design right. The key insight is that Playwright already does the hard part in creating and serialising the handles. All this code is really doing is creating a clever proxy that allows you to use it as the original synchronous API in a fluent way which is actually all async underneath. Of course you have to await before you get a value but it's still much nicer that awaiting at each step. I'm very happy with how this turned out. The rest are the helpers to make it easy to add it as a test runner.

Now this is even more code so I know where this is going... well at least it is here for posterity. On your earlier question, with this version there actually isn't any changes to the original code so it likely is a lot easier to maintain as a separate library. I'll have to work on that next.

[steinybot]

Deleted as I switched it to use npm workspaces with a shared lock file in the root.

[steinybot]

It might not be the best idea to commit these but I figured I would leave them here for the review just to prove that it works.

[steinybot]

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