feat: cache spot prices for consecutive calls

[orestiseth]

Note

Introduce an in-memory TTL cache and use it to cache spot price lookups (30s), updating assets use cases, wiring, and tests; bump snap version.

• Assets pricing:
  • Caching spot prices: AssetsUseCases now uses a cache (ICache) to store spot prices for 30s, avoiding repeated lookups; refactors fetching loop and deduplicates by ticker.
  • Wiring: index.ts instantiates InMemoryCache and passes it to AssetsUseCases.
• Store:
  • New cache: Add ICache interface and InMemoryCache implementation with TTL, bulk ops, and expiration handling.
• Tests:
  • Add comprehensive tests for InMemoryCache.
  • Update AssetsUseCases.test.ts to mock cache and verify caching behavior.
• Manifest:
  • Bump packages/snap/snap.manifest.json version to 1.3.0 and update shasum.

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