Batch-fetch oracle prices for multiple assets in a single invocation.
Calls lastprice(self, asset) on the FXDao Reflector oracle for each asset.
Uses this contract's own address as the requester — the oracle calls
require_auth() on it, which succeeds because a contract automatically
authorizes calls it makes.
fn get_prices(
env: soroban_sdk::Env,
oracle: soroban_sdk::Address,
assets: soroban_sdk::Vec,
) -> soroban_sdk::Map>