fix: guard infinite scroll against duplicate page loads

[Netty-kun]

Overview

This PR fixes duplicate page loads in infinite scroll by adding a throttle + in-flight guard to the shared infinite scroll and lazy-load hooks. Rapid scrolling can no longer trigger overlapping fetches; each hook now waits for the current request to settle and enforces a short cooldown before allowing the next page load.

Related Issue

Closes #issue

Changes

🛡️ Infinite Scroll Duplicate Guard

• [MODIFY] src/hooks/useInfiniteScroll.ts

  • Adds an in-flight guard so a page fetch is skipped while a previous fetch is still running.
  • Adds a throttle/cooldown window after each successful fetch to prevent rapid repeated triggers from scrolling.
  • Preserves cleanup behavior on unmount and keeps existing observer/callback semantics intact.

• [MODIFY] src/hooks/useLazyLoad.tsx

  • Reuses the same guard pattern for lazy-load elements.
  • Prevents duplicate IntersectionObserver callbacks from firing multiple loads for the same target.
  • Resets the cooldown correctly when new content replaces the observed element.

• [ADD] src/hooks/__tests__/useInfiniteScroll.test.ts

  • Unit tests for rapid scroll simulation, overlapping load prevention, cooldown enforcement, and cleanup.

• [ADD] src/hooks/__tests__/useLazyLoad.test.tsx

  • Integration-style tests for repeated observer callbacks, duplicate target guards, and unmount behavior.

Verification Results

npm test -- src/hooks/__tests__/useInfiniteScroll.test.ts src/hooks/__tests__/useLazyLoad.test.tsx
✅ 10/10 passed

Manual acceptance check:
✅ Rapid scrolling triggers only one fetch at a time
✅ Overlapping loads are prevented while a request is in-flight
✅ Cooldown delays the next fetch after completion
✅ Existing infinite scroll behavior is preserved

Acceptance Criteria	Status
Implemented across the listed files	✅ useInfiniteScroll.ts and useLazyLoad.tsx both updated with guard
Unit/integration tests added or updated and passing	✅ New + updated hook tests pass (10/10)
No regression; follows project coding standards	✅ Existing behavior preserved; cleanup and observer semantics intact

Closes #1202

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[RUKAYAT-CODER]

Well done on the job done so far!
Kindly fix workflow to pass