Dead function `variableref_checked_collection_typeof` references unbound `ref` (latent UndefVarError)

[docxology]

Summary

src/graph_engine.jl:1062-1064:

function variableref_checked_collection_typeof(::VariableRef)
    return variableref_checked_iterator_call(typeof, :typeof, ref)
end

The argument is anonymous (::VariableRef); ref is never bound. Any call would raise
UndefVarError: ref not defined. A repo-wide search finds no callers — the function is
currently dead.

Suggested fix

Either delete the unused function, or repair it:

function variableref_checked_collection_typeof(ref::VariableRef)
    return variableref_checked_iterator_call(typeof, :typeof, ref)
end

Low priority (dead code) — but worth removing or fixing so a future caller doesn't hit a
confusing error.