feat: get plan bulk with cache

[hj24]

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Summary

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Checklist

• 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

[gemini-code-assist]

Summary of Changes

Hello @hj24, 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 implements a new, highly efficient, and resilient caching layer for retrieving tenant subscription plans in bulk. By introducing get_plan_bulk_with_cache, the system can now leverage Redis to store and retrieve plan data, significantly reducing the number of calls to the external billing API, especially in batch processing scenarios. The implementation includes sophisticated logic to manage cache consistency, handle Redis operational failures, and validate cached data, ensuring reliable plan retrieval. Furthermore, the existing bulk plan fetching method has been made more robust by adding error handling that allows it to continue processing valid plans even when encountering malformed data for specific tenants.

Highlights

• New Cached Billing Plan Retrieval: Introduced get_plan_bulk_with_cache in BillingService to fetch tenant subscription plans, utilizing Redis for caching to reduce direct billing API load.
• Robust Caching Logic: The new caching mechanism handles various scenarios including cache hits, misses, partial hits, and gracefully falls back to the billing API upon Redis errors or invalid cached data.
• Enhanced Error Handling for Bulk Plans: Improved the existing get_plan_bulk method to log and skip individual invalid tenant plans during bulk retrieval, preventing a single malformed entry from failing the entire batch.
• Comprehensive Test Coverage: Added extensive integration tests for the new caching functionality, covering edge cases like Redis failures, invalid cache data, and TTL expiration, alongside a new unit test for the improved get_plan_bulk error handling.

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[gemini-code-assist]

Code Review

This pull request introduces a caching layer for bulk fetching tenant plans, which is a great feature for improving performance and reducing load on the billing API. The implementation is solid, using Redis mget and pipelines for efficient batch operations, and includes robust error handling and fallbacks. The accompanying integration tests are comprehensive and cover many edge cases, which is excellent.

I have a couple of minor suggestions to improve code clarity and style. One is about simplifying a redundant exception handler, and the other is a small style fix in the new tests.

[hjlarry]

LGTM