Get balances across multiple yields and networks

Retrieve balances for multiple wallet addresses across different networks and yield opportunities. Send an array of balance requests - each request can specify a yieldId (optional for chain scanning), address, network, and custom arguments. This is the same format as the single yield balance endpoint but in array form. Duplicate requests (same yieldId + address + network) are automatically deduplicated, with specific yield requests taking precedence over chain scans.