feat(core): add middleware execution ordering

[zouyx]

AgentScope-Java Version

2.0.1-SNAPSHOT

Description

Closes #2449

Adds MiddlewareBase.order() with a default priority of 1.

ReActAgent.Builder.build() now performs one stable descending sort after all user and automatic middleware registrations. Higher numeric values are outermost; equal priorities retain registration order.

Also adds core/Harness coverage and updates Chinese and English middleware documentation.

Validation:

mvn -pl agentscope-core,agentscope-harness -am \
  -Dtest=ReActAgentNewLoopBuilderTest,HarnessMiddlewareOrderTest \
  -Dsurefire.failIfNoSpecifiedTests=false test

Checklist

Please check the following items before code is ready to be reviewed.

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated (e.g. links, examples, etc.)
• Code is ready for review

[gemini-code-assist]

Caution

The consumer version of Gemini Code Assist on GitHub has been sunset. All code review activity has officially ceased.

[Copilot]

Pull request overview

Adds an explicit middleware ordering mechanism to AgentScope-Java so middleware execution can be prioritized deterministically (while keeping registration order stable for ties), with accompanying tests and documentation updates.

Changes:

• Introduces MiddlewareBase.order() (default 1) as the standard middleware priority hook.
• Sorts registered middlewares once during ReActAgent.Builder.build() using a stable descending sort by order().
• Adds/updates core + harness tests and updates English/Chinese middleware documentation to describe the ordering behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
docs/v2/zh/docs/building-blocks/middleware.md	Documents the new order()-based execution ordering (Chinese).
docs/v2/en/docs/building-blocks/middleware.md	Documents the new order()-based execution ordering (English).
agentscope-harness/src/test/java/io/agentscope/harness/agent/HarnessMiddlewareOrderTest.java	Adds harness-level coverage to validate ordering interactions with harness middlewares.
agentscope-core/src/test/java/io/agentscope/core/agent/ReActAgentNewLoopBuilderTest.java	Adds core-level coverage for descending + stable tie behavior.
agentscope-core/src/main/java/io/agentscope/core/ReActAgent.java	Applies a stable descending sort of middlewares by MiddlewareBase.order() during build.
agentscope-core/src/main/java/io/agentscope/core/middleware/MiddlewareBase.java	Adds the new order() API with Javadoc describing its semantics.