fix: improve rate limiter concurrency

[devin-ai-integration]

Improve Rate Limiter Concurrency

This PR improves the rate limiter's concurrency handling to ensure exactly 100 requests are processed before blocking additional requests.

Changes

• Removed global mutex for better concurrency
• Using atomic operations for accurate counting
• Changed blocking logic to allow exactly MaxRequests
• Added concurrent test cases
• Improved window reset logic with atomic operations

Test Results

Load test with 150 concurrent requests shows proper rate limiting:

Status code distribution:
  [200] 100 responses  # First 100 requests processed successfully
  [429] 50 responses   # Additional requests blocked as expected

Implementation Details

1. Storage Implementation:

   • Using sync.Map for thread-safe storage
   • Atomic operations for request counting
   • Thread-safe window reset logic

2. Rate Limiter:

   • Removed unnecessary global mutex
   • Process exactly MaxRequests before blocking
   • Accurate request counting under high load

3. Testing:

   • Added concurrent test cases
   • Verified with hey tool under high load
   • All tests passing

Link to Devin run: https://app.devin.ai/sessions/edf66e27ee6c4cbf8f70bafca9e24b04
Requested by: Wesley

[devin-ai-integration]

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