Cache improvement

[sonic182]

I think using :ets instead of a GenServer with Map.new is a better choice because:

• Concurrency: :ets allows multiple processes to read and write simultaneously without bottlenecks.
• Performance: It provides constant-time lookups and avoids message passing overhead.
• Memory efficiency: Data is stored outside the process heap, reducing GC pressure and improving scalability.

AS backend for https://github.com/os6sense/DefMemo/blob/master/lib/defmemo_result_table_gs.ex

Also, ttl would be nice to have isn't it?