[api] Swap Quote Auto Max Quantity, Misc Fee Fixes

1. Resolves #1655 (closed).
2. Fixes liquidity fee amounts on streaming swap quotes (amount was not properly multiplied by quantity).
3. Fixes swap slippage calculation - previously we would sum the slips from swap events in a double swap quote, which became increasingly inaccurate with larger swaps. Instead this computes the slippage as liquidity_fee / (final_emit + liquidity_fee).
4. Similar to swap slippage, loan slippage now calculated based on weighted slip of repayment and outbound liquidity fees.