RFC: Middleware Appliers for Third Party Middlewares

[Nick-Lucas]

A problem we continue to have with the experimental standalone middlewares, and also t.middleware, is that they have caused many bugs with type inference over time, and so compose unreliably. It's not clear that all problems are solvable.

This is an approach which draws inspiration from other libraries like Tanstack Router, and simply doesn't try to fight the typescript type system by making everything into a function call of known type

I copied over the minimal example project for this prototype so the diff looks bigger than it should, focus on:

• AcmeMiddleware.ts: https://github.com/trpc/trpc/pull/5112/files#diff-860c9b23a905a4f6494e0cf370a317bde88b6e702ba3cb26db9ba79115fb1b78
• trpc.ts: https://github.com/trpc/trpc/pull/5112/files#diff-9cfcb5afca1d1d2518a9465e6aba2367ea9e39aa0236e19a634a7b1a13854341
• index.ts: https://github.com/trpc/trpc/pull/5112/files#diff-ebbbc5e7b43d53fbdc9a56f8f3125a6470d7dcfc7ce4114a4402d63f3e591f99
• the shared Next type: https://github.com/trpc/trpc/pull/5112/files#diff-28374e196350161477845434683132162955a507c4d6ff3bebad3774ebb0749d

🎯 Changes

What changes are made in this PR? Is it a feature or a bug fix?

✅ Checklist

• I have followed the steps listed in the Contributing guide.
• If necessary, I have added documentation related to the changes made.
• I have added or updated the tests related to the changes made.

[Nick-Lucas]

Closed in favour of #5294

[github-actions]

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