Fix Java 21 compatibility issues by replacing getFirst() with get(0)#348

Copilot wants to merge 3 commits intocodex/create-expiration-event-class-and-methodstcheeric/nostr-java:codex/create-expiration-event-class-and-methodsfrom

copilot/fix-fd0f53e6-4cc6-43c7-980b-8ce0771805eftcheeric/nostr-java:copilot/fix-fd0f53e6-4cc6-43c7-980b-8ce0771805efCopy head branch name to clipboard