feat(snap-networks-utils): move cache utils into shared lib

[taran-a]

Explanation

Extracts the duplicated caching layer shared by the Solana, Tron, and Stellar snaps into @metamask/snap-networks-utils.

New utils/cache/ module in @metamask/snap-networks-utils, exported from the root entry point:

• ICache, CacheEntry, TimestampMilliseconds — generic cache contract (identical across all three snaps)
• InMemoryCache — TTL-backed in-memory cache
• StateCache — cache backed by a snap state manager, typed against a new minimal structural CacheStateManager interface (getKey/setKey/update) so each snap's existing IStateManager satisfies it without modification
• useCache / useCacheUntil — function-wrapping helpers with fixed-TTL and dynamic-expiry caching, including stellar's refreshCache option, serialize()-based default key generation, and tron's fix that consults the cache when the in-memory expiry map is empty (so still-valid entries survive a snap restart)

References

• Related to WPN-1635

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

[sonarqubecloud]

Quality Gate failed

Failed conditions
17.1% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud