Non-fallible iteration and Inspect::inspect

Currently method `Inspect::inspect` is fallible, because we expect that user code implementing it would need to do iterations and thus require fallibility, because iteration is fallible. This feels like a design smell of iteration API to me, and I think it is worth revisiting.

Start by tracing the Inspect::inspect implementation and the iteration API to understand why iteration requires fallibility. The issue is complete only when the project has an agreed design for reconciling non-fallible inspection with iteration, along with its resulting implementation scope.

Written by the indexing model from the issue text.