feat: integrate the OpenNext server

[vicb]

@dario-piotrowicz @james-elicx @petebacondarwin Here is what I have been working on.
/cc @conico974 - I will never thank you enough for all the support!

disclaimers:

• it's a preview on an "experimental" branch :)
• I have updated the README

I have only updated the middleware example, this is how I test it (from examples/middleware):

OPEN_NEXT_DEBUG=1 node /path/to/opennextjs-cloudflare/packages/cloudflare/dist/cli/index.mjs
wrangler dev

You might see errors related to the cache - it is expected (this PR has more info)

There is still some cleanup to do:

• Added "TODO" from this PR - more generally drop legacy stuff and migrate all to ON
• fix(cache): make dummy cache error ignorable opennextjs-aws#641 mentioned above
• Update all the examples and make sure tests pass
• Drop tsup and use tsc directly (as in aws)
• Figure out how to handle ON ALS override
• Probably some more that I can't remember right now

Then we should work on the cache implementation.

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pnpm add https://pkg.pr.new/@opennextjs/cloudflare@140

commit: 2efdc83