feat: support context builder?

[tclain-pillar]

Thanks for the phenomenal work. Having used trpc, I can't wait to have a native nextjs solution.

Something that works well in trpc is the notion of a context builder. We can build the authentication state for instance and provide the current user for all query mutation automatically.

I know we could do that on every query mutation manually / and or with an Higher Order Function but I am wondering if there is any plan to have that in scope.

How can I help ?