🐛 修复 PayloadType 缺失 Heartbeat 类型

[shoucandanghehe]

问题

PayloadType 未包含 Heartbeat 类型，导致 receive_payload() 收到服务器发送的心跳请求时（op=1），无法正确反序列化为 Heartbeat 实例。

结果是 _loop() 中的 Heartbeat 分支永远不可达：

elif isinstance(payload, Heartbeat):
    # 当接受到心跳payload时...
    await self._heartbeat(ws, bot)

修复

将 Heartbeat 添加到 PayloadType 的 Union 类型中。

 PayloadType: TypeAlias = (
     Annotated[
-        Dispatch | Reconnect | InvalidSession | Hello | HeartbeatAck,
+        Dispatch | Heartbeat | Reconnect | InvalidSession | Hello | HeartbeatAck,
         Field(discriminator="opcode"),
     ]
     | Payload
 )

验证

• 运行 ruff check 通过
• 运行 ruff format --check 通过

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.78%. Comparing base (9c5dabe) to head (3800739).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #81   +/-   ##
=======================================
  Coverage   74.78%   74.78%           
=======================================
  Files          38       38           
  Lines        7067     7067           
  Branches      372      372           
=======================================
  Hits         5285     5285           
  Misses       1715     1715           
  Partials       67       67           

Flag	Coverage Δ
unittests	74.78% <ø> (ø)

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