feat(gemini): add support for thought signatures in Gemini 3 Pro Preview

[QIN2DIM]

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Related Issues or Context

fixed: #2088

This commit enables the capture and propagation of thought signatures from the Gemini 3 Pro Preview model, allowing for better tracking of reasoning steps and intermediate thoughts during model execution.

• Updated manifest.yaml and google.yaml to reflect 'Gemini dev' label and version 0.6.1
• Modified gemini-3-pro-preview.yaml to enforce temperature = 1.0 as required by the model
• Enhanced LLM implementation to extract and attach thought signatures to message content
• Added debug logging and print statements for tracing thought signature flow
• Updated message parsing to preserve thought signatures across different content types (text, code, execution results)
• Added support for interleaved thinking via thought_signature handling

Documentation: https://ai.google.dev/gemini-api/docs/gemini-3?hl=zh-cn&thinking=high#thought_signatures

This PR contains Changes to Non-Plugin

• Documentation
• Other

This PR contains Changes to Non-LLM Models Plugin

• I have Run Comprehensive Tests Relevant to My Changes

This PR contains Changes to LLM Models Plugin

• My Changes Affect Message Flow Handling (System Messages and User→Assistant Turn-Taking)

• My Changes Affect Tool Interaction Flow (Multi-Round Usage and Output Handling, for both Agent App and Agent Node)

• My Changes Affect Multimodal Input Handling (Images, PDFs, Audio, Video, etc.)

• My Changes Affect Multimodal Output Generation (Images, Audio, Video, etc.)

• My Changes Affect Structured Output Format (JSON, XML, etc.)

• My Changes Affect Token Consumption Metrics

• My Changes Affect Other LLM Functionalities (Reasoning Process, Grounding, Prompt Caching, etc.)

• Other Changes (Add New Models, Fix Model Parameters etc.)

Version Control (Any Changes to the Plugin Will Require Bumping the Version)

• I have Bumped Up the Version in Manifest.yaml (Top-Level Version Field, Not in Meta Section)

Dify Plugin SDK Version

• I have Ensured dify_plugin>=0.3.0,<0.6.0 is in requirements.txt (SDK docs)

Environment Verification (If Any Code Changes)

Local Deployment Environment

• Dify Version is: , I have Tested My Changes on Local Deployment Dify with a Clean Environment That Matches the Production Configuration.

SaaS Environment

• I have Tested My Changes on cloud.dify.ai with a Clean Environment That Matches the Production Configuration