test(amp): cover future adapter contracts

[simPod]

Context

The AMPHP future adapter needs an explicit behavior contract before its implementation can be optimized.

Decision

Add contract tests only. The adapter implementation is intentionally unchanged.

Consequences

• Demonstrates that the current adapter already satisfies the nested Future, rejection, iterable aggregate, and aggregate-settlement behaviors used by the optimization work.
• Lets the implementation change be evaluated as behavior-preserving.
• Prevents future changes from regressing these semantics.

Related to webonyx#1954