Elixir GenServer callbacks and concurrency

3-Second Blueprint (English)

1. GenServer's handle_call processes synchronous requests, blocking the caller until it returns a {:reply, value, state} tuple.
2. handle_cast executes asynchronous fire-and-forget updates, returning :ok immediately while updating process state concurrently.
3. handle_info captures raw out-of-band messages via Process.send, while Supervisors monitor and restart failed GenServers.