[Bug] buildWithinGenerations()

[smasongarrison]

buildWithinGenerations() claims to accept beta = "optimized" / "indexed", but it passes that value down to helpers that do if (beta) (e.g., createGenDataFrame()), which will error for non-logical values. Either restrict beta to a strict logical (and update error text/docs), or normalize string aliases to TRUE/FALSE before calling downstream functions.

Originally posted by @Copilot in #109