Handle encoding and decoding errors in a middleware-like extension point

### Question

I'd like to add telemetry to my app to report issues where an API response is missing a required key or otherwise has decoding errors. Ideally I could write middleware to achieve this, but from what I've been able to tell, middleware can't intercept decoding errors.

In a perfect world, the server handling the API requests would always return 100% spec-compliant responses, never introducing breaking changes, but mistakes happen.

How would you suggest I add this telemetry to my client application using `swift-openapi-*`?

Start by reviewing the generated client decoding path and the middleware-like extension points in the swift-openapi-* packages. Determine where missing required keys and other decoding errors can be observed, then define an extension mechanism that lets applications report this telemetry without changing generated API behavior.

Written by the indexing model from the issue text.