Elixir: Use `:persistent_term` instead of ETS

[Qqwy]

Changes:

• Use :persistent_term for lookups instead of :ets
• Use for :lists.map instead of Enum.map when iterating over the result lists.
• Use atoms instead of small strings in the result maps.
• Less defensive pattern matching in places where we already know the shape of the result data.
• Properly configure the full logger to :warning level (rather than only the :console backend), ensuring that lower-level log output is not evaluated only to be discarded.

This PR should be fully compatible with #13 and #11.