fn get_apy(env: soroban_sdk::Env) -> u32
fn initialize(
env: soroban_sdk::Env,
token_contract_id: soroban_sdk::Address,
savings_contract_id: soroban_sdk::Address,
)
Called only by the savings contract. reward = principal * 5% * (duration / 100_000)
fn calculate_and_pay(
env: soroban_sdk::Env,
user: soroban_sdk::Address,
principal: i128,
duration_ledgers: u32,
)