chore(stellar): use shared cache utils

[taran-a]

Explanation

Migrates the Stellar snap to the shared caching utilities in @metamask/snap-networks-utils and removes its local copies (src/services/cache/)

Behavioral changes:

• useCacheUntil consults the cache when the in-memory expiry map is empty (expiresAt === undefined || now < expiresAt) instead of requiring the map to be populated — Tron's fix, adopted by the shared version. Latent for Stellar today (its InMemoryCache survives nothing), but correct if a persisted cache is ever wired.
• Error logging: both wrappers take an optional logger (default silent); call sites pass the snap logger to preserve current output. The stray 'useCache' prefix Stellar's local useCacheUntil applied is gone.

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 passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud