[Shredder401k]

Add test coverage for previously untested areas

Closes #924
Closes #925
Closes #926
Closes #927

Changes

Added comprehensive test coverage for:

• Horizon transaction fetching (hooks/use-stream-history.ts)

  • Maps Horizon records to history entries
  • Handles HTTP errors and empty results

• Stream cache invalidation (hooks/use-streams.ts)

  • invalidateStreams() triggers refetch across all subscribed hooks
  • Verifies cache clearing behavior

• Single stream hook (hooks/use-streams.ts)

  • useStream() loading states and refetch behavior
  • Error handling and empty ID edge cases

• RPC retry helpers (lib/contract.ts)

  • isRetryableError() error classification
  • fetchWithRetry() and withRetry() retry logic with exponential backoff
  • Uses fake timers to verify retry delays

Test Files

• __tests__/hooks/use-stream-history.test.ts (new)
• __tests__/hooks/use-streams.test.ts (added tests)
• __tests__/lib/contract-retry.test.ts (new)

All tests follow existing Vitest + Testing Library patterns and pass with npm test.

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You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

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