fix: use LRUMap for all in-memory caches

[arcoraven]

PR-Codex overview

This PR focuses on optimizing various cache implementations by replacing Map with LRUMap from the mnemonist library across multiple files, enhancing memory efficiency and performance.

Detailed summary

• Changed accessTokenCache from Map to LRUMap.
• Changed smartWalletsCache from Map to LRUMap.
• Changed webhookCache from Map to LRUMap.
• Changed _accountsCache from Map to LRUMap.
• Changed sdkCache from Map to LRUMap.
• Changed walletsCache from Map to LRUMap.
• Changed keypairCache from Map to LRUMap.

✨ Ask PR-Codex anything about this PR by commenting with /codex {your question}