Compute BBO and NBBO from order data

You are given a list data of order records. Each record is a 4-tuple:

(exchange_id, price, quantity, order_type)

• exchange_id : string/int identifying the exchange
• price : positive number
• quantity : positive integer
• order_type : either "B" (bid/buy) or "A" (ask/sell)

Implement a class QuoteBook initialized with data, supporting:

1. get_exchange_bbo(exchange_id) -> (best_bid, best_ask)
   • Returns the best bid and best ask for that exchange.
2. get_nbbo() -> (best_bid, best_ask)
   • Returns the national best bid and offer (NBBO) across all exchanges.

Definitions:

• Best bid : highest bid price.
• Best ask : lowest ask price.
• If there are multiple orders at the same best price on the relevant scope (exchange or all exchanges), treat the displayed quantity as the sum of quantities at that best price .
• If a side does not exist (no bids or no asks), return None for that side.

Return format:

• best_bid and best_ask should each be either None or a tuple (price, total_quantity_at_price) .

Constraints/expectations:

• len(data) can be large (e.g., up to 10^5 or more), so repeated calls to these methods should be efficient.