fix: consolidate duplicate rate limiter implementations

[REHAN-503]

Description

Fixes #1797

This PR consolidates the application's rate-limiting implementation by removing the standalone middleware-specific rate limiter and reusing the existing RateLimiter class across the codebase.

What changed

• Removed the standalone rateLimit() implementation from lib/rate-limit.ts
• Added a dedicated middlewareRateLimiter instance using the existing RateLimiter class
• Refactored middleware.ts to use middlewareRateLimiter.checkWithResult()
• Updated affected unit tests to align with the unified implementation
• Preserved the existing middleware policy of 60 requests per minute

Why

The repository contained two separate rate-limiting implementations:

1. RateLimiter class backed by DistributedCache / TTL-based storage
2. Standalone rateLimit() function used by middleware

Pillar

• Bug Fix
• Core Feature

Checklist

• My branch is up to date with the latest changes required for this PR
• I have tested my changes locally
• Production build passes successfully
• TypeScript compilation passes successfully
• Updated related tests where necessary
• No unrelated files or dependency changes were included

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[github-actions]

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[github-actions]

⚠️ Hey @REHAN-503, this PR has merge conflicts with the main branch.

Please pull the latest changes and resolve the conflicts so we can review it!

git fetch origin
git rebase origin/main
# resolve any conflicts, then:
git push --force-with-lease

Once resolved, the needs-rebase label will be removed automatically on the next check. 🙌

[Aamod007]

LGTM! Consolidating the rate limiter is a clean refactor.

[github-actions]

👋 Hey @REHAN-503! Thanks for your contribution! 🎉

Unfortunately, this PR has been automatically closed because it is not linked to any open issue.

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