Extract a pluggable, multi-instance-safe RateLimitStore abstraction

[NkechiOgbuji]

Close #307

Description

This PR refactors the rate limiting implementation by introducing a pluggable RateLimitStore abstraction, separating the token-bucket algorithm from its storage implementation.

The default behavior remains unchanged through an in-memory store, while making it straightforward to introduce a shared backend (such as Redis) for multi-instance or serverless deployments without modifying the core rate-limiting logic.

Linked Issue

Closes #307

Type of Change

• Bug fix (UI or API integration)
• New feature / component
• UI/UX improvement
• Documentation update
• Chore / refactor / dependency update
• Tests only

Changes Made

• Introduced a RateLimitStore abstraction to decouple storage from the token-bucket algorithm.
• Added InMemoryRateLimitStore as the default implementation to preserve existing behavior.
• Refactored rateLimitRequest to work with an injected store while maintaining backward compatibility.
• Updated integration API routes to use the refactored rate limiter.
• Extended the rate-limit test suite to validate the algorithm against an injectable store implementation.
• Updated deployment documentation with an example of how a shared store (for example, Redis) can be integrated for production deployments.

Validation

• Focused rate-limit tests pass.
• Touched files pass TypeScript checks.
• git diff --check reports no whitespace or merge-marker issues.
• Existing repository-wide failures are pre-existing baseline issues unrelated to this change.

Notes

This refactor preserves the existing rate-limiting behavior and public API while providing a clean extension point for future shared storage implementations. No new dependencies were introduced.