List all variables and their tables
list_variables.RdReturns a tibble mapping all variables (raw ACS variables and
computed indicators) to their construct-level table name. This provides a
comprehensive view of every variable that compile_acs_data() produces
for registered tables. Variables from unregistered ACS tables passed as
raw codes (e.g., "B25070") are not included here; they are
auto-generated at runtime.