devex-rates: Roblox Developer Exchange (DevEx) rates as data

Roblox Developer Exchange (DevEx) rates as structured data: the three rates in force (standard $0.0038, U.S. 18+ $0.0054, legacy $0.0035 per Earned Robux), every rate change on record since 2013 with its source, the 30,000 Earned Robux minimum, and a dependency-free Luau module that does the arithmetic. Roblox does not publish a rate archive. The data is re-verified against Roblox's documentation at least every 45 days and is maintained alongside the rate history at LootTally's DevEx rates page. Data: CC BY 4.0. Code: MIT.