Add a target-forwarding behavior, including a lazy target

[kzu]

Summary

Ship a behavior that forwards an invocation to another instance, including a target created on first use. This is the decorator, the interface proxy with a target, and the virtual proxy used by ORMs.

API

The behavior holds either an instance or Func<object?>. Each applicable call invokes the same member on that instance and returns its result, including arguments, ref / out values, and exceptions.

The factory runs on the first forwarded call and the instance is reused after that. The factory may return another stunt.

Constraints

• Invoke the target through the compiled call shape. Native AOT has no reflection fallback for an arbitrary member.
• An interface stunt has no base body, so a result requires a target. A class stunt with no target calls the base implementation.
• Virtual calls from a base constructor already enter the pipeline. The factory must be safe to run from that call.

Acceptance

• An interface stunt forwards arguments and the return value to a hand-written implementation, and a thrown exception reaches the caller.
• The factory runs once.
• A class stunt with no target still runs the base implementation.

Composition

Outer to inner, the recommended pipeline is observation, resilience, transaction, cache, then this forwarder.