address differences in variable availability over time

[wcurrangroome]

Variables are not consistently available over time. For example, B25074_051 (household income by gross rent...) is not available pre-2014, at least not by the same variable name. Auto-documentation should create a variable dependency object. Then, compile_acs_data should read this variable dependency and compare variable availability for each requested year. When a variable is not available for some or all years, it should be included with all NAs, and this should be reflected in the metadata and returned to the user as a warning.

[wcurrangroome]

Variable name changes are available at the following for 2020-2022: https://www.census.gov/data/developers/data-sets/acs-5year.2022.html#list-tab-1806015614. Assessing variable changes pre-2020 may be more challenging.