Every place where a type/function name is used in a Humility API should allow fully-qualified names.

Rust programs often use the same name in different modules, because we have modules/namespaces. e.g. a typical program will contain many types named Error in different places.

Humility originally stripped crate/module path information off types, and used unqualified names. This has been causing problems for a while in things like processing Idol interfaces -- see https://github.com/oxidecomputer/hubris/issues/1896 for the most recent case.

I added partial support for fully qualified names back in 2021, but we need to complete the switch-over. It's okay to allow unqualified names in some cases (particularly in the TUI!) but that should be a convenience, which turns into an error if the name is ambiguous. At that point the user should always be able to provide a fully qualified name.

Start by tracing Humility's partial fully qualified-name support and the API call sites that accept type or function names; the issue does not name specific files or tests. Map where unqualified names remain and define how ambiguity should become an error, while preserving convenient TUI lookup. Done means every Humility API location can accept fully qualified names.