feat(gemini): add baseUrl builder support

[rrrjqy66]

AgentScope-Java Version

1.0.12-SNAPSHOT

Description

Background

Issue #1127 requests a simpler way to configure a custom baseUrl for Gemini.

The underlying Google GenAI SDK already supports endpoint override through HttpOptions, but AgentScope-Java currently exposes that only through the lower-level httpOptions(...) builder method. As a result, Gemini is less ergonomic than the other model builders when users need to target a custom gateway, private endpoint, or mock server.

Purpose

Add a first-class baseUrl builder entrypoint for Gemini so custom endpoints can be configured more easily and consistently.

Changes Made

• Added GeminiChatModel.Builder.baseUrl(String)
• Mapped builder-level baseUrl to the effective Google GenAI HttpOptions
• Preserved existing httpOptions(...) settings when both httpOptions(...) and baseUrl(...) are provided
• Updated Gemini documentation examples in both English and Chinese docs
• Added unit coverage for baseUrl(...) and the merge behavior with existing httpOptions(...)

Why this approach

This change is intentionally kept narrow and focused on the builder ergonomics requested in #1127.

The Google GenAI SDK already models endpoint override through HttpOptions, so this PR adds a convenient high-level entrypoint without changing the underlying transport model. Advanced transport or proxy-related configuration remains available through the existing lower-level configuration methods.

How to Test

• Build a GeminiChatModel with .baseUrl(https://example.test) and verify construction succeeds
• Build a model with both .httpOptions(...) and .baseUrl(...) and verify the custom base URL is applied without losing the other HTTP settings
• Run mvn -pl agentscope-core -Dtest=GeminiChatModelTest test
• Run mvn -pl agentscope-core test
• Run mvn -pl agentscope-core spotless:check

Checklist

• Code has been formatted with mvn spotless:apply
• All tests are passing (mvn test for the affected module)
• Javadoc comments are complete and follow project conventions
• Related documentation has been updated
• Code is ready for review

Closes #1127

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...java/io/agentscope/core/model/GeminiChatModel.java	83.33%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

[Copilot]

Pull request overview

Adds a higher-level baseUrl(...) builder option to GeminiChatModel so users can override the Gemini API endpoint without needing to construct HttpOptions manually, aligning Gemini’s ergonomics with other model builders in the codebase.

Changes:

• Added GeminiChatModel.Builder.baseUrl(String) and merged it into effective Google GenAI HttpOptions.
• Ensured baseUrl(...) overrides only the base URL while preserving other httpOptions(...) settings.
• Updated English/Chinese docs and added unit tests covering the new builder behavior.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
agentscope-core/src/main/java/io/agentscope/core/model/GeminiChatModel.java	Adds baseUrl builder field/method and merges it into effective HttpOptions used by the Google GenAI client.
agentscope-core/src/test/java/io/agentscope/core/model/GeminiChatModelTest.java	Adds unit tests validating baseUrl wiring and merge behavior with existing HttpOptions.
docs/en/task/model.md	Documents the new baseUrl option and provides an example.
docs/zh/task/model.md	Documents the new baseUrl option and provides an example (Chinese docs).

Comments suppressed due to low confidence (1)

agentscope-core/src/main/java/io/agentscope/core/model/GeminiChatModel.java:100

• Adding baseUrl into the public GeminiChatModel constructor signature is a source/binary breaking change for any callers using new GeminiChatModel(...). To keep backward compatibility, consider keeping the old constructor (without baseUrl) and delegating it to the new one with baseUrl = null (optionally deprecating the old overload).

    public GeminiChatModel(
            String apiKey,
            String baseUrl,
            String modelName,
            boolean streamEnabled,
            String project,
            String location,
            Boolean vertexAI,
            HttpOptions httpOptions,