Optimise Horizon API calls with request batching and deduplication

[Marvell69]

Multiple components on the same page often make identical Horizon API calls independently. Deduplicating and batching these calls reduces API load and improves page performance.

Requirements and context

• Audit all Horizon API calls in the app
• Implement request deduplication: identical in-flight requests share a single promise
• Batch multiple address lookups (balance, federation) where Horizon supports it
• Cache responses with appropriate TTLs (balances: 30s, federation: 10min, events: 60s)
• Document expected API call reduction in PR

Suggested execution

git checkout -b perf/horizon-request-deduplication

• Create src/lib/horizonClient.ts with deduplication and caching
• Replace direct Horizon calls with the client
• Write tests for deduplication and cache behaviour

Example commit message
perf: deduplicate and batch Horizon API calls across the app