Add a Polly resilience behavior

[kzu]

Summary

Adapt a Polly ResiliencePipeline to IStuntBehavior. Retry, circuit breaker, timeout, rate limiter, fallback, hedging, and chaos stay in Polly.

API

A behavior constructed with ResiliencePipeline. It runs next through Polly's execute API.

For awaitable members, use Proceed so each Polly attempt awaits the Task or ValueTask and observes its fault. A synchronous exception and a faulted awaitable both count as a failed attempt.

Keep the Polly reference optional, in a companion package, so Stunts itself does not depend on Polly.

Constraints

• Use Polly's Native AOT surface. Do not reflect over T to read a task result.
• Recommended order, outer to inner: observation, this resilience behavior, then inside each attempt the transaction and the cache, then the target.

Acceptance

• A retry strategy invokes the target again after a throw or a faulted task, then returns the successful value.
• A fallback strategy can supply a result without a further target call.
• The behavior adds no retry loop of its own.

[kzu]

Might be a sample, definitely not built-in.