fix(core): stream 取消时释放上游订阅

[guslegend0510]

变更说明

修复 AgentBase 在 stream() 被下游取消时没有释放上游订阅的问题。
之前下游 Flux 取消后，上游 Mono 仍可能继续运行，导致执行资源无法及时释放，出现“鬼任务”或后续调用被阻塞的情况。

本次改动包括：

• 在 AgentBase#createEventStream 中将上游订阅绑定到 sink.onDispose(...)
• 取消流时及时 dispose 上游订阅
• 保持原有的流式输出行为不变
• 补充 AgentBaseTest，覆盖“取消流后释放执行锁、后续可继续调用”的场景

另外，顺带修复了 ToolCallParam copy builder 的一个既有编译问题，保证当前分支可正常编译和测试。

验证

• mvn -B -pl agentscope-core -am spotless:check
• mvn -B -pl agentscope-core -am "-Dtest=AgentBaseTest,ToolCallParamTest" -DfailIfNoTests=false test
• mvn -B -T1 clean verify
  其中失败点来自仓库里已有的外部依赖/环境相关测试，不是本次改动引入的

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[AgentScopeJavaBot]

🤖 AI Review

This PR correctly fixes the stream cancellation resource leak in AgentBase.createEventStream. Before this change, when a downstream subscriber cancelled the Flux returned by stream(), the upstream Mono subscription was orphaned — the execution lock was never released, blocking all subsequent agent calls. The fix uses Reactor's Disposable.Swap + sink.onDispose(...) to bind the upstream subscription lifetime to the downstream sink. The implementation is idiomatic Reactor. The test is well-designed using StepVerifier.thenCancel(). The secondary ToolCallParam copy-builder fix is a genuine compilation bugfix.

[LearningGp]

[guslegend0510]

@LearningGp 我已经解决了这个冲突，麻烦再审查一下，谢谢

[chickenlj]

Thanks. Please check #1796