Function base64 

pub(crate) fn base64(bytes: &[u8]) -> String

Base64, so the wasm can live inside the page.

The same twenty lines as solium-animation’s preview builder, and a deliberate copy rather than a shared helper: sharing it would mean this crate depending on that one, and the empty [dependencies] is what keeps an effect testable without a compositor. Twenty lines with RFC 4648’s own vectors under them is the cheaper half of that trade.