fix(agent): 对齐 EventType.ALL 的文档与流式行为

[guslegend0510]

做了什么

• 明确 EventType.ALL 和 StreamOptions#getEventTypes() 实际会包含 AGENT_RESULT
• 同步更新英文/中文流式文档，和真实行为保持一致
• 补充回归测试，验证 EventType.ALL 会流式输出 AGENT_RESULT

原因

• Issue EventTypes针对ALL的注释和实际代码实现逻辑不相符 #1439 指出注释/文档与实现不一致
• 这次只统一说明与测试，不修改运行时逻辑

验证

• mvn -pl agentscope-core spotless:apply
• mvn -pl agentscope-core -Dtest=StreamOptionsTest test

Fixes #1439

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[LearningGp]

If we confirm that the AGENT_RESULT event should be included in ALL, the Javadoc for AGENT_RESULT itself should also be updated accordingly.
PTAL @chickenlj

[guslegend0510]

@LearningGp 麻烦审核，一下，谢谢

[AgentScopeJavaBot]

🤖 AI Review

This PR correctly updates the AGENT_RESULT Javadoc to reflect that it is streamed by default (because StreamOptions defaults use EventType.ALL and shouldStream() returns true for any type when ALL is present). However, the fix is incomplete: the ALL constant's own Javadoc at line 97 still says "Special value to stream all event types (except AGENT_RESULT)" — the exact same misinformation this PR aims to correct. Additionally, the PR description claims to update English/Chinese streaming docs and add regression tests, but neither appears in the diff. The streaming docs (docs/v1/en/docs/task/streaming.md lines 46-47 and docs/v1/zh/docs/task/streaming.md lines 46-47) still state AGENT_RESULT is "not included in stream by default" and ALL means "all the above (except AGENT_RESULT)". Please fix these remaining inconsistencies so the documentation alignment is complete.