One-time init: set admin and initial EAR (parts-per-billion, e.g. 85_000_000 for 8.5%)
fn init(env: soroban_sdk::Env, admin: soroban_sdk::Address, ear_ppb: u64)
Admin-only: update EAR (ppb)
fn set_ear_ppb(env: soroban_sdk::Env, admin: soroban_sdk::Address, ear_ppb: u64)
Read EAR (ppb) and last updated timestamp (unix seconds)
fn get_ear_ppb(env: soroban_sdk::Env) -> (u64, u64)