feat(models): add support for gemini server tools (#2241)

[pony-huang]

AgentScope-Java Version

[The version of AgentScope-Java you are working on, e.g. 1.0.12, 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]

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

Simple

public class Main {
    public static void main(String[] args) throws JsonProcessingException {

        GeminiChatModel gemini =
                GeminiChatModel.builder()
                        .modelName("gemini-3.5-flash")
                        .streamEnabled(true)
                        .serverTools(List.of(GeminiServerTool.googleSearch().build()))
                        .build();

        Toolkit toolkit = new Toolkit();
        WeatherTools weatherTools = new WeatherTools();
        toolkit.registerTool(weatherTools);
        ReActAgent agent =
                ReActAgent.builder()
                        .name("weather-agent")
                        .model(gemini)
                        .toolkit(toolkit)
                        .maxIters(6)
                        .build();

        Msg response =
                agent.call(
                                new UserMessage(
                                        """
                                        What is the southernmost city in the China? What's the weather like there today?\
                                        """))
                        .block();

        assert response != null;
        System.out.println(response.getTextContent());
        System.out.println(new ObjectMapper().writeValueAsString(response.getMetadata()));
    }

    static final class WeatherTools {

        @Tool(
                name = "getWeather",
                description = "Get the weather in a given location",
                readOnly = true)
        public String getWeather(
                @ToolParam(
                                name = "location",
                                description = "The city and state, e.g. San Francisco, CA",
                                required = true)
                        String location) {

            System.out.println("getWeather called with location: " + location);
            return """
            {
              "response": "Very hot. it's  96.8°F",
            }
            """;
        }
    }
}

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[codecov]

Codecov Report

❌ Patch coverage is 81.42857% with 52 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...extensions/model/gemini/tool/GeminiServerTool.java	71.62%	10 Missing and 11 partials ⚠️
...s/model/gemini/formatter/GeminiResponseParser.java	77.27%	11 Missing and 4 partials ⚠️
...scope/extensions/model/gemini/GeminiChatModel.java	61.53%	3 Missing and 2 partials ⚠️
...e/src/main/java/io/agentscope/core/ReActAgent.java	40.00%	3 Missing ⚠️
...scope/core/agent/accumulator/ReasoningContext.java	82.35%	2 Missing and 1 partial ⚠️
...model/gemini/formatter/GeminiMessageConverter.java	95.38%	0 Missing and 3 partials ⚠️
...va/io/agentscope/core/message/ToolResultBlock.java	81.81%	2 Missing ⚠️

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