refactor(ratelimit): use RateLimitError for 429 response

[sanket1035]

Description

Resolves #164.

Refactors the rate limiting middleware in backend/middleware/rate_limit.py to use the centralized RateLimitError class from utils.errors.

Changes Included:

• backend/middleware/rate_limit.py:
  • Imported RateLimitError from utils.errors.
  • Refactored rate_limit_exceeded_handler to instantiate RateLimitError with retry_after payload and generate response using .to_dict().
  • Standardized JSON response format: { "error": "...", "code": "RATE_LIMITED", "retry_after": ..., "payload": { "retry_after": ... } }.
  • Preserved the HTTP Retry-After header.
• backend/middleware/error_handler.py:
  • Delegated 429 error handler directly to rate_limit_exceeded_handler.
• backend/tests/test_rate_limit.py:
  • Added assertion for "code": "RATE_LIMITED" in 429 response body format test.

How to Test

Run pytest from backend/:

pytest tests/test_rate_limit.py
pytest tests/test_error_handling.py

[vercel]

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[Him-an-shi]

@sanket1035 please resolve merge conflicts

[sanket1035]

Solved please check out @Him-an-shi