Implement Redis-Backed Rate Limiting

[adityapichikala]

Description

Migrated the rate limiter to use fastapi-limiter with a Redis backend to ensure scalability and persistence across container restarts.

• Implemented a dynamic fallback dependency (dynamic_rate_limiter) that gracefully falls back to the existing in-memory deque if the Redis connection fails or isn't configured.
• Moved the rate limit check from a global middleware to a router-level Depends block, ensuring it only targets the heavy AI endpoints.
• Added a redis container to docker-compose.yml and updated .env.example.

Related Issue

Fixes #443

Type of change

• Bug fix
• New feature / enhancement
• Documentation update
• Test addition
• Refactor

Checklist

• I have read CONTRIBUTING.md
• My branch is up to date with main
• I have run pytest -v and all tests pass
• I have not introduced duplicate issues or features
• My PR title follows the format: feat/fix/docs/test: short description
• I have added tests for new features (Level 2 and 3 issues)
• No hardcoded secrets or API keys in my code
• This PR is linked to a GSSoC 2026 issue

Screenshots (if frontend change)

N/A (Backend logic only)

Test evidence

pytest -v
# ... (omitting verbose initialization) ...
tests/test_ai_provider.py::test_call_llm_success PASSED                  [  0%]
tests/test_ai_provider.py::test_call_llm_timeout_retries PASSED          [  1%]
# ... (omitting middle tests for brevity) ...
tests/test_python_ast_analyzer.py::test_detects_division_by_zero_inside_function_call PASSED [ 96%]
tests/test_python_ast_analyzer.py::test_detects_out_of_range_list_index PASSED [ 96%]
tests/test_python_ast_analyzer.py::test_detects_out_of_range_string_index PASSED [ 97%]
tests/test_python_ast_analyzer.py::test_detects_string_integer_concatenation PASSED [ 98%]
tests/test_share.py::test_create_and_fetch_share PASSED                  [ 99%]
tests/test_share.py::test_expired_share_returns_404 PASSED               [100%]

============================== warnings summary ===============================
..\..\..\..\..\AppData\Roaming\Python\Python314\site-packages\fastapi\testclient.py:1
  C:\Users\adity\AppData\Roaming\Python\Python314\site-packages\fastapi\testclient.py:1: StarletteDeprecationWarning: Using `httpx` with `starlette.testclient` is deprecated; install `httpx2` instead.
    from starlette.testclient import TestClient as TestClient  # noqa

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
======================= 128 passed, 1 warning in 6.81s ========================

[adityapichikala]

hi @imDarshanGK ,
would please check this and verify,if any changes are required i will be doing it

[imDarshanGK]

@adityapichikala update your branch with the latest main changes and resolve conflicts

[adityapichikala]

hi @imDarshanGK ,
check it out ,everything is set