perf(message): optimize message loading and reduce SQL queries

[hundredwz]

Summary

• Optimize messages loading logic to reduce database queries
• Change service_api message fetching order to match docs (descending order)

Fixes #13723

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Checklist

Important

Please review the checklist below before submitting your pull request.

• This change requires a documentation update, included: Dify Document
• I understand that this PR may be closed in case there was no previous discussion or issues. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

[crazywoola]

Please open an issue or link an existing issue in the description.

[hundredwz]

Please open an issue or link an existing issue in the description.

Thanks for the reminder! I've created an issue #13723 to track this performance optimization work.