Improve dependency graph validation

[ZacSweers]

Dependency graph validation could be improved! Currently lattice does validation in one pass and then separately collects bindings that need provider fields. These provider fields are then sorted by codependency to determine init order. This is performant enough but is a little messy. I'd love to streamline this with a little inspiration from dagger, where we track "field generators" while validating the graph and "visit" those generators during our recursion.

Generators would have an internal state of uninitialized, initializing, deferred, and initialized. Every time we visit a type, we get or create a generator and "visit" it. If a generator is reentrantly visited while initializing, it means we have a cycle. If it's a valid cycle, we mark it as deferred and these types will need to use DelegateFactory.

At the end, we collect generators. There may be some duplications from each dfs pass, and in those cases we take either the one that uses delegate factory or any. Generators that result in fields in the end must be one of

• Scoped (and wrapped in DoubleCheck)
• Backed by a DelegateFactory
• Used by multiple dependencies

Finally, any deferred fields will also need a corresponding initializer in the constructor.

If we keep insertion order of these generators as they're visited, my hope is we can infer the init order directly from that (i.e. reverse the order they were added).