Refactor Mobilizon.Federation.ActivityPub and add typespecs

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/mobilizon/addresses/address.ex

@@ -73,6 +73,7 @@ defmodule Mobilizon.Addresses.Address do
     put_change(changeset, :url, url)
   end
 
+  @spec coords(nil | t) :: nil | {float, float}
   def coords(nil), do: nil
 
   def coords(%__MODULE__{} = address) do
@@ -81,6 +82,7 @@ defmodule Mobilizon.Addresses.Address do
     end
   end
 
+  @spec representation(nil | t) :: nil | String.t()
   def representation(nil), do: nil
 
   def representation(%__MODULE__{} = address) do