Match Buy and Sell Orders from an Order Book

Question

## Problem

Given a list of order book entries — each with `type` (BUY/SELL), `price`, and `quantity` — implement an order matching function that returns all **matched trades**.

Matching rules:
- A BUY order at price P matches the lowest SELL order with price ≤ P
- A SELL order at price P matches the highest BUY order with price ≥ P
- Partial fills are allowed (remaining quantity stays in the book)

## Example
```
orders = [
  {type:BUY,  price:102, qty:10},
  {type:SELL, price:100, qty:8},
  {type:SELL, price:101, qty:5},
]
Output: [{buy:102, sell:100, qty:8}, {buy:102, sell:101, qty:2}]
```

## Expected data structures
- BUY side: max-heap by price
- SELL side: min-heap by price

## Follow-up
How do you handle orders with the same price? (FIFO queue per price level)