fix: fix dialyzer in GRPC.Server.Supervisor

Found dialyzer error on master branch:

lib/grpc/server/supervisor.ex:39:callback_spec_type_mismatch
The @spec return type does not match the expected return type
for init/1 callback in Supervisor behaviour.

Actual:
@spec init(...) :: 
  {:ok,
   {{:one_for_all, non_neg_integer(), pos_integer()}
    | {:one_for_one, non_neg_integer(), pos_integer()}
    | {:rest_for_one, non_neg_integer(), pos_integer()}
    | {:simple_one_for_one, non_neg_integer(), pos_integer()}
    | %{
        :auto_shutdown => :all_significant | :any_significant | :never,
        :intensity => non_neg_integer(),
        :period => pos_integer(),
        :strategy => :one_for_all | :one_for_one | :rest_for_one | :simple_one_for_one
      },
    [
      {_, {atom(), atom(), :undefined | [any()]}, :permanent | :temporary | :transient,
       :brutal_kill | timeout(), :supervisor | :worker, :dynamic | [atom()]}
      | %{
          :id => _,
          :start => {atom(), atom(), :undefined | [any()]},
          :modules => :dynamic | [atom()],
          :restart => :permanent | :temporary | :transient,
          :shutdown => :brutal_kill | timeout(),
          :significant => boolean(),
          :type => :supervisor | :worker
        }
    ]}}

Expected:
@spec init(...) :: 
  :ignore
  | {:ok,
     {%{
        :intensity => non_neg_integer(),
        :period => pos_integer(),
        :strategy => :one_for_all | :one_for_one | :rest_for_one
      },
      [
        {_, {atom(), atom(), :undefined | [any()]}, :permanent | :temporary | :transient,
         :brutal_kill | timeout(), :supervisor | :worker, :dynamic | [atom()]}
        | %{
            :id => _,
            :start => {atom(), atom(), :undefined | [any()]},
            :modules => :dynamic | [atom()],
            :restart => :permanent | :temporary | :transient,
            :shutdown => :brutal_kill | timeout(),
            :significant => boolean(),
            :type => :supervisor | :worker
          }
      ]}}

________________________________________________________________________________
done (warnings were emitted)
Halting VM with exit status 2

The sup_flags() type introduced in Elixir 1.14. So I create a new type in GRPC.Server.Supervisor module to support earlier versions.

elixir-grpc / grpc

fix: fix dialyzer in GRPC.Server.Supervisor #282