test(c-lsp): regression for #220 (C++ CALLS attributed to function)

#220: C++ CALLS edges originated from the Module node instead of the
enclosing Function, breaking function-level trace_path. The cross-LSP
resolver now sets caller_qn = enclosing_func_qn; the test asserts a call
(doWork→helper) is attributed to doWork, not the module.

Closes #220.