fix(formatter): preserve multimodal DataBlock handling

[guslegend0510]

AgentScope-Java Version

2.0.0-SNAPSHOT

Description

Background

In the multimodal message pipeline, DataBlock(image/png) could be normalized incorrectly and end up being treated as plain text, which breaks legacy media block handling for providers.

Changes

• Added unified media normalization in MediaUtils.
• Updated formatter/converter logic for OpenAI, Anthropic, DashScope, Gemini, and Ollama to preserve multimodal DataBlock handling.
• Adjusted base formatter media detection to use the unified media kind logic.
• Added/updated regression tests for media normalization and Ollama/DashScope formatter paths.

Testing

• mvn -pl agentscope-core -Dtest=OllamaMessageConverterTest,OllamaChatFormatterTest,OllamaConversationMergerTest,OllamaMultiAgentFormatterTest test

Related Issues

• Fixes [Bug]: Multimodal messages are not recognized by the model #1782

Checklist

• 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 64.51613% with 88 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ope/core/formatter/ollama/OllamaChatFormatter.java	46.42%	10 Missing and 5 partials ⚠️
...re/formatter/ollama/OllamaMultiAgentFormatter.java	53.57%	4 Missing and 9 partials ⚠️
.../core/formatter/ollama/OllamaMessageConverter.java	40.00%	8 Missing and 4 partials ⚠️
.../core/formatter/gemini/GeminiMessageConverter.java	63.63%	2 Missing and 6 partials ⚠️
...rmatter/dashscope/DashScopeConversationMerger.java	60.00%	2 Missing and 4 partials ⚠️
...formatter/dashscope/DashScopeMessageConverter.java	66.66%	2 Missing and 4 partials ⚠️
.../core/formatter/openai/OpenAIMessageConverter.java	58.33%	2 Missing and 3 partials ⚠️
.../java/io/agentscope/core/formatter/MediaUtils.java	91.83%	1 Missing and 3 partials ⚠️
...formatter/anthropic/AnthropicMessageConverter.java	66.66%	1 Missing and 3 partials ⚠️
...ore/formatter/gemini/GeminiConversationMerger.java	60.00%	1 Missing and 3 partials ⚠️
... and 5 more

📢 Thoughts on this report? Let us know!

[AgentScopeJavaBot]

🤖 AI Review

[chickenlj]

Please check the CI failures.

[guslegend0510]

@chickenlj CI 已经通过了，麻烦审核一下，谢谢您