Function class 

pub fn class(err: &EngineError) -> ErrorClass

Classification of err using the ScriptError-aware table.

Delegates to EngineError::class() for non-Transport variants; for Transport, downcasts the inner source to ScriptError and delegates to ScriptError::class(). Non-Valkey transport errors (no ScriptError inside) default to Terminal — retrying an unknown-shape error is unsafe.