refactor: replace genAI model sdk by okHttp

[Aias00]

AgentScope-Java Version

[The version of AgentScope-Java you are working on, e.g. 1.0.2, check your pom.xml dependency version or run mvn dependency:tree | grep agentscope-parent:pom(only mac/linux)]

Description

[Please describe the background, purpose, changes made, and how to test this PR]
Introduce dedicated DTOs for Gemini API request and response structures and update related components.
fixes #96

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

[codecov]

Codecov Report

❌ Patch coverage is 57.93651% with 318 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...java/io/agentscope/core/model/GeminiChatModel.java	46.25%	59 Missing and 20 partials ⚠️
...e/formatter/gemini/dto/GeminiGenerationConfig.java	27.05%	62 Missing ⚠️
...entscope/core/formatter/gemini/dto/GeminiPart.java	56.47%	37 Missing ⚠️
...pe/core/formatter/gemini/GeminiResponseParser.java	56.79%	17 Missing and 18 partials ⚠️
...scope/core/formatter/gemini/dto/GeminiRequest.java	36.58%	26 Missing ⚠️
...scope/core/formatter/gemini/GeminiToolsHelper.java	74.60%	9 Missing and 7 partials ⚠️
...ore/formatter/gemini/GeminiConversationMerger.java	60.71%	9 Missing and 2 partials ⚠️
...entscope/core/formatter/gemini/dto/GeminiTool.java	60.86%	9 Missing ⚠️
...ope/core/formatter/gemini/GeminiChatFormatter.java	75.86%	6 Missing and 1 partial ⚠️
.../core/formatter/gemini/GeminiMessageConverter.java	78.12%	4 Missing and 3 partials ⚠️
... and 7 more

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[Copilot]

Pull request overview

This PR replaces the Google GenAI Java SDK with dedicated DTOs and direct HTTP calls to the Gemini API, simplifying the implementation and removing dependencies on the Google SDK and Vertex AI support.

• Custom DTOs introduced for all Gemini API request/response structures
• Direct HTTP implementation using OkHttp with SSE streaming support
• All formatters, converters, and parsers updated to use new DTOs

Reviewed changes

Copilot reviewed 32 out of 32 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
GeminiChatModel.java	Replaced SDK client with OkHttpclient for direct API calls with streaming support
GeminiRequest.java, GeminiResponse.java	New DTOs for API request/response structures
GeminiContent.java, GeminiPart.java	DTOs for message content and parts
GeminiTool.java, GeminiToolConfig.java	DTOs for tool definitions and configuration
GeminiGenerationConfig.java	DTO for generation parameters
GeminiChatFormatter.java	Updated to work with DTOs instead of SDK types
GeminiMessageConverter.java	Updated conversion logic for new DTOs
GeminiMediaConverter.java	Updated media handling to use DTO Blob type
GeminiToolsHelper.java	Simplified tool conversion without SDK schema conversion
GeminiResponseParser.java	Updated response parsing for new DTO structures
ModelProviderType.java	Simplified Gemini config removing Vertex AI parameters
AgentScopeProducer.java	Removed Vertex AI configuration logic
pom.xml (core)	Removed google-genai dependency
pom.xml (mem0)	Added jackson-datatype-jsr310 dependency
Test files	Updated all tests to use new DTOs instead of SDK types

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[Aias00]

gemini-2.0-flush

gemini-3-pro-preview

[Copilot]

Pull request overview

Copilot reviewed 38 out of 38 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

agentscope-extensions/agentscope-extensions-mem0/pom.xml:1

• The jackson-datatype-jsr310 version 2.15.2 may be outdated. Consider using a more recent version that matches the Jackson version used elsewhere in the project, or verify if 2.15.2 is the intended version for compatibility reasons.

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[AlbumenJ]

Please make sure all the E2E Tests pass

[AlbumenJ]

Your current logic for handling the Base URL differs from the GenAI SDK's approach, specifically regarding the handling of the GOOGLE_API_BASE_URL key.