feat: fluent extensions, throws extension, gen static interfaces

[jasonkuhrt]

This PR is a major re-architecting of the generator system motivated by pursuing best possible (practical) IDE performance.

The major change is moving as much as possible to generation time:

• request methods are now generated, no more mapped types to derive them
• selection sets are now generated interfaces, no more mapped types to derive them

One disadvantage of this approach is that extensions will not have core schema types that are fully dog-fooded internally as well. That drift may lead to core schema types being removed (because they become unused internally) or a degree toward there. Perhaps a way to make up for this is enabling extensions to tap into the CLI generator. For example OrThrow emitting types instead of using in-memory type transformations.

One unintentional advantage is that we now can generate awesome JSDoc. This is actually a significant benefit in its own right.

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Additional work on this PR came about in order to re-realize the OrThrow extension. I devised a way to extend the fluent chain in a type-safe way that I'm actually rather proud of (perf seems ok too!). Internally now each fluent method is actually entirely modular and that ability now gets exposed to extensions. Therefore we changed the OrThrow extension into something much simpler that just adds a chaining method called throws(). Everything about it became simpler and its IDE perf is much better too. 🤩

Also closes #1104