Feature: Lazy Evaluation Ergonomics

[Goldziher]

Focused Scope

Improve lazy-evaluation ergonomics and documentation around the existing use() API.

Proposed v1

• Document use(async () => ...) with buildAsync().
• Add tests showing async use() resolves through buildAsync().
• Ensure sync build() fails clearly when async lazy values are used.
• Optionally add lazy as an alias for use if the naming improvement is worth the public API surface.

Out of Scope

• Field dependency graphs.
• lazyIf() or conditional DSLs.
• New relationship/association semantics.

Conditional values can already be expressed in the factory function through kwargs and hooks.