feat: Increase API concurrency control to avoid service downtime

[Flynn-Zh]

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Modification

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[Copilot]

Pull request overview

This PR adds concurrency control to the FastAPI service to prevent service overload by limiting the number of concurrent requests being processed. The implementation uses an asyncio semaphore with a configurable maximum concurrent request limit.

Key changes:

• Added a global semaphore-based concurrency limiter controlled by the max_concurrent_requests parameter
• Applied concurrency limiting to the /file_parse endpoint using FastAPI dependencies
• Disabled API documentation endpoints (OpenAPI, Swagger UI, ReDoc)

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[Flynn-Zh]

copilot review 有一部分是合理的，一部分是看似合理，其实是瞎说，合理的部分已修改 @myhloli