Batch-fetch oracle prices for multiple assets in a single invocation.
Calls lastprice(requester, asset) on the FXDao Reflector oracle for
each asset, returning a map of asset → price data.
fn get_prices(
env: soroban_sdk::Env,
oracle: soroban_sdk::Address,
requester: soroban_sdk::Address,
assets: soroban_sdk::Vec,
) -> soroban_sdk::Map>