`Eternal.Supervisor.start_link/3` does not support input unless `ets_opts` contains `:named_table`

[HansGlimmerfors]

(Opening this issue in correlation with https://github.com/whitfin/eternal/pull/6, in case the PR is not merged)

Eternal.Supervisor.start_link/3 shows that :ets.new/2 is supposed to return a Eternal.Table.t(), but the typespecs don't match. :ets.new/2 returns atom | tid() whereas Eternal.Table.t() is defined as number | atom. The difference in typespecs shows up when trying to call Eternal.Supervisor.start_link/3 without passing :named_table in ets_opts, as Eternal.Table.to_name/2 is unable to handle the returned value from :ets.new/2: