initial the create_time to actual timestamp

[Osier-Yi]

📝 PR Type

• Add new sample
• Update existing sample
• Add new test cases
• Fix test failures
• Documentation/Configuration update

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📚 Description

Resolve an issue where MockSession created MockMessage instances without a valid timestamp. The session now supplies a real (UTC) timestamp by default.

related issue: #108

🧪 Testing Validation

[Please explain how to validate the changes:

1. How to run the added/modified test cases?
2. Is integration testing with agentscope required?
3. Has code been formatted (e.g., pre-commit)?]

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✅ Checklist

Please complete the following checks before submitting the PR:

• All sample code has been formatted with pre-commit run --all-files
• All new/modified test cases have passed (run pytest tests/)
• Test coverage has not decreased (if applicable)
• Sample code follows agentscope best practices (e.g., config management, logging)
• Related documentation in agentscope-samples has been updated (e.g., README.md)

[gemini-code-assist]

Summary of Changes

Hello @Osier-Yi, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where mock message instances were created without valid timestamps. It ensures that MockFileBase and MockMessage objects are initialized with accurate UTC timestamps, improving data consistency and addressing the related issue #108. Additionally, the MockMessage class has been refactored into a dataclass with improved default field initialization.

Highlights

• Timestamp Initialization: The create_time and update_time fields in both MockFileBase and MockMessage classes are now correctly initialized with the current UTC timestamp using datetime.now(timezone.utc).isoformat(), replacing the static placeholder 'xxxyyy'.
• MockMessage Class Enhancement: The MockMessage class has been converted into a dataclass. Its id field now uses uuid.uuid4 as a default factory, and the files field uses a list default factory, ensuring proper default initialization for mutable types.

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[gemini-code-assist]

Code Review

This pull request resolves an issue with mock messages having invalid timestamps by initializing create_time and update_time with the actual UTC timestamp. The changes correctly use dataclasses.field with a default_factory to generate timestamps. Additionally, you've correctly addressed mutable default arguments for id and files in MockMessage by converting it to a dataclass and using default_factory.

I've added one suggestion to improve maintainability by reducing code duplication for the timestamp generation logic. Overall, this is a good improvement.

[xieyxclack]

LGTM