refactor: unified execution report stream replacing split putOrder/putTrade callbacks

[Copilot]

The notification system had separate putOrder (two overloads) and putTrade callbacks, making it fragmented and hard to consume as a coherent event stream. This replaces them with a single onExecutionReport(const ExecutionReport&) callback modelled after FIX protocol Execution Report (msg type 8).

New types (include/types.hpp)

• ExecType enum: New | Rejected | Canceled | Trade
• ExecutionReport flat struct — single message type for all events; fields are conditionally populated based on exec_type:
  • Order events (New, Rejected, Canceled): msg_type, order_id, status, qty, original_qty, error
  • Trade events: maker_order_id, taker_order_id, maker_status, taker_status, last_qty, last_price
• Removed the now-redundant Trade struct

Interface (include/types.hpp)

NotificationInterface and EmptyNotification now expose a single entry point:

void onExecutionReport(const ExecutionReport& report);

OrderBook (include/orderbook.hpp)

All dispatch sites use C++20 designated initializers for clarity:

notification_.onExecutionReport(ExecutionReport{
    .exec_type     = ExecType::Trade,
    .maker_order_id = mOrderID,
    .taker_order_id = tOrderID,
    .maker_status  = mStatus,
    .taker_status  = tStatus,
    .last_qty      = qty,
    .last_price    = price,
});

Tests (test/util.cpp)

Collapsed the NotificationBase / OrderNotification / Trade polymorphic hierarchy into a plain vector<ExecutionReport>. The to_string rendering preserves the existing assertion format so no test strings change.

[Copilot]

Pull request overview

This PR refactors the order book notification API from separate putOrder / putTrade callbacks into a single unified onExecutionReport(const ExecutionReport&) stream, aligning event delivery around a FIX-style execution report model.

Changes:

• Introduces ExecType and a unified ExecutionReport struct (replacing the old Trade struct) and updates the notification interface to onExecutionReport(...).
• Updates OrderBook dispatch sites to emit ExecutionReport instances (using C++20 designated initializers).
• Simplifies test notifications to store a vector<ExecutionReport> and preserves existing assertion string formatting via a renderer.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
include/types.hpp	Adds ExecType + ExecutionReport and replaces the notification API with onExecutionReport(...).
src/types.cpp	Adds stream rendering (operator<<) for ExecType.
include/orderbook.hpp	Updates all notification dispatch sites to emit unified ExecutionReport events.
test/util.cpp	Refactors test notification capture to store ExecutionReport objects and renders them back to the legacy assertion strings.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.