chore: 移除应用层心跳，升级为协议层保活与死链检测

[joesdu]

📝 描述 (Description)

• 客户端/服务端全面移除 Heartbeat* 相关选项与实现，统一采用 .NET 8+ KeepAliveInterval/KeepAliveTimeout 进行协议层 PING/PONG 保活与死链检测
• 新增接收分发队列（ReceiveDispatchQueueCapacity），接收循环与用户回调彻底解耦，慢处理器不再阻塞接收与保活检测，队列满时自动背压
• 服务端支持 MaxMessageSize，超限主动断连，防御内存耗尽
• 优化 SendTextAsync 内存分配，关闭连接增加超时保护，所有 API 保持线程安全
• 客户端/服务端 README、XML 注释、参数校验等文档全面更新，去除应用层心跳说明，推荐协议层保活配置
• 单元测试同步调整，移除 HeartbeatResponseMessage 配置

🔗 相关问题 (Related Issues)

• Closes #
• Fixes #

🏷️ 变更类型 (Type of Change)

• 🐛 错误修复 (Bug fix) (non-breaking change which fixes an issue)
• ✨ 新功能 (New feature) (non-breaking change which adds functionality)
• 💥 破坏性变更 (Breaking change) (fix or feature that would cause existing functionality to not work as expected)
• 📚 文档更新 (Documentation update)
• 🔧 重构 (Refactor) (no functional changes)
• 🧪 测试 (Tests) (adding or updating tests)
• 🛠️ 构建/CI 变更 (Build/CI changes)
• 🎨 样式变更 (Style changes) (formatting, etc.)
• 🚀 性能改进 (Performance improvements)
• 🔒 安全改进 (Security improvements)

✅ 检查清单 (Checklist)

• 我的代码遵循项目的编码标准 (My code follows the project's coding standards)
• 我已经对自己的代码进行了自我审查 (I have performed a self-review of my own code)
• 我已经在难以理解的区域注释了我的代码 (I have commented my code, particularly in hard-to-understand areas)
• 我已经对文档进行了相应的更改 (I have made corresponding changes to the documentation)
• 我的更改不会产生新的警告或错误 (My changes generate no new warnings or errors)
• 我已经添加了证明我的修复有效或我的功能工作的测试 (I have added tests that prove my fix is effective or that my
  feature works)
• 新增和现有的单元测试在本地通过我的更改 (New and existing unit tests pass locally with my changes)
• 任何依赖变更都已合并并发布到下游模块 (Any dependent changes have been merged and published in downstream modules)

🧪 测试 (Testing)

• 单元测试 (Unit tests)
• 集成测试 (Integration tests)
• 手动测试 (Manual testing)
• 其他 (请指定) (Other (please specify)):

📸 截图 (如果适用) (Screenshots (if applicable))

🔍 附加说明 (Additional Notes)

[Copilot]

Pull request overview

EN: Summary

This PR refactors EasilyNET’s WebSocket client/server to fully remove application-level heartbeat messages and rely on .NET 8+ protocol-level keep-alive (PING/PONG) for liveness, while also adding receive/dispatch decoupling and max inbound message size enforcement to improve robustness and prevent memory exhaustion.

Changes:

• Remove Heartbeat* options/logic and switch to KeepAliveInterval + KeepAliveTimeout (protocol-level) on both client and server.
• Introduce a bounded receive-dispatch queue (ReceiveDispatchQueueCapacity) to decouple receive loops from user callbacks with backpressure.
• Add/strengthen max message size handling (server closes on oversize) and update docs/tests accordingly.

EN: Key issues

• The sample TestMode flag is effectively forced to true and will run the background test service unconditionally.
• ReceiveDispatchQueueCapacity is used to construct a bounded channel but lacks an explicit validation path on the server side, which can lead to confusing runtime exceptions.
• WebSocketClientOptions XML docs describe keep-alive behavior as sending “PONG” when interval is set alone; this is misleading and should be corrected.

EN: Suggested changes

• Restore TestMode to default-off (or gate it via configuration / compilation symbol).
• Add explicit validation for ReceiveDispatchQueueCapacity near channel creation with a clear exception.
• Correct XML docs to describe periodic PING frames when only KeepAliveInterval is set.

---

中文：总结

该 PR 对 EasilyNET 的 WebSocket 客户端/服务端进行了统一升级：彻底移除应用层 Heartbeat（业务 ping/pong 消息），改为使用 .NET 8+ 提供的协议层 KeepAlive（PING/PONG）实现保活与死链检测；同时通过接收-分发队列解耦，避免慢处理器阻塞接收循环，并加入/完善 MaxMessageSize 以防止内存耗尽攻击；文档与测试也同步更新。

变更点：

• 移除 Heartbeat* 相关配置与实现，统一使用 KeepAliveInterval + KeepAliveTimeout。
• 新增 ReceiveDispatchQueueCapacity，接收循环与用户回调解耦，队列满时背压。
• 服务端超限主动断连（MessageTooBig），并同步更新 README/XML 注释/单测。

中文：主要问题

• sample 里的 TestMode => !false 等价于永远开启测试模式，会导致后台测试服务在任何环境都执行。
• 服务端侧 ReceiveDispatchQueueCapacity 缺少显式校验，配置为 0/负数会在运行时抛出不直观异常。
• WebSocketClientOptions 注释对 KeepAliveInterval 单独配置时的行为描述为 “PONG”，易误导使用者。

中文：修改建议

• 将 sample 的测试模式恢复为默认关闭，或改为配置开关/编译条件控制。
• 在服务端 WebSocketSession 构造处对 ReceiveDispatchQueueCapacity 做明确校验并抛出清晰异常信息。
• 修正注释为：仅设置 KeepAliveInterval 时运行时周期性发送 PING，但不会因超时中止连接。

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/EasilyNET.Test.Unit/WebSocket/ManagedWebSocketClientTest.cs	Update tests to remove HeartbeatResponseMessage usage.
test/EasilyNET.Test.Unit/WebSocket/ManagedWebSocketClientMaxMessageSizeTest.cs	Adjust max-message-size tests after heartbeat removal.
src/EasilyNET.WebCore/WebSocket/WebSocketSessionOptions.cs	Replace heartbeat options with MaxMessageSize, receive-dispatch queue, and keep-alive options.
src/EasilyNET.WebCore/WebSocket/WebSocketSession.cs	Add receive/dispatch decoupling, max-size checks, close timeout handling, and send allocation tweaks.
src/EasilyNET.WebCore/WebSocket/README.md	Rewrite docs to reflect protocol-level keep-alive and new session semantics.
src/EasilyNET.WebCore/Middleware/WebSocketMiddleware.cs	Pass KeepAliveInterval/Timeout via WebSocketAcceptContext.
src/EasilyNET.Core/WebSocket/WebSocketClientOptions.cs	Remove heartbeat options; add keep-alive timeout + receive-dispatch queue capacity; update validation/docs.
src/EasilyNET.Core/WebSocket/README.md	Update client documentation to protocol-level keep-alive and new dispatch semantics.
src/EasilyNET.Core/WebSocket/ManagedWebSocketClient.cs	Add persistent dispatch loop and remove heartbeat filtering/loop; improve send and state/close semantics.
sample/WebApi.Test.Unit/BackgroundServices/WebSocketClientTestService.cs	Update sample client to use protocol-level keep-alive; (currently forces test mode on).

[Copilot]

Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.