perf(trending): memoize campaign heuristic calculations

[JemimahEkong]

Summary

Optimizes the Trending Campaigns hook by memoizing heuristic calculations to prevent unnecessary recomputation during unrelated component re-renders.

Closes #832

Changes

• Updated src/hooks/useTrendingCampaigns.ts:

  • Wrapped getTrendingCampaigns(campaigns, limit) with useMemo.
  • Added dependencies for campaigns and limit.
  • Preserved existing trending score calculations and ranking behavior.

• Added src/__tests__/hooks/useTrendingCampaigns.test.tsx:

  • Verified trending order remains unchanged.
  • Added coverage for memoization behavior.
  • Confirmed recomputation occurs when campaigns data or limit changes.
  • Covered loading, error, and refetch passthrough behavior.

Validation

• ✅ All 35 hook tests passing across 9 suites.
• ✅ All 12 trending-related tests passing.
• ✅ No changes to trending scoring factors or ranking logic.
• ✅ Only computation frequency was optimized.

Notes

This change only improves performance by avoiding repeated heuristic calculations when the campaigns reference and limit remain unchanged. No user-facing behavior or trending results are modified.

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[sshdopey]

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