fix: optimize unique document filtering with set

[y-omr]

Checklist:

Important

Please review the checklist below before submitting your pull request.

• Please open an issue before creating a PR or link to an existing issue
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods

Description

In this refactoring, I made the following improvements:

Simplification of Duplicate Loops:

In the original code, dify_documents and external_documents were processed separately, leading to redundancy. After refactoring, the entire documents list is processed in a single loop with branching based on the provider.

Efficient Management of Unique Documents:

To manage unique document IDs, I changed the data structure from a list to a set (doc_id). Using a set allows for faster duplicate checks (O(1)), thereby enhancing performance.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update, included: Dify Document
• Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• Dependency upgrade

Testing Instructions

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Test A
• Test B