Optimize identity fetching

[BraydenLangley]

Description of Changes

• Reuses the same client across searches so ContactsManager's in-memory cache persists instead of being discarded on every call.
• New searches abort previous in-flight requests via AbortController + Promise.race, preventing stale queries from blocking the UI
• Debounce increased from 300ms → 400ms to reduce redundant network requests
• LRU cache optimized
• Request ID system ensures only the latest query's results are applied to state

Testing Procedure

I have tested locally while linked to peerpay and have observed performance / UX improvements.

• I have tested manually in my local environment

Checklist:

• I have performed a self-review of my own code
• I have run npm version patch so that my changes will trigger a new version to be released when they are merged

[BraydenLangley]

Merge pending new ts-sdk version