Move require Logger to module level

Move require Logger statements from function/case level to module level
for better code organization and consistency with Elixir best practices

lib/mv/membership/member/validations/email_not_used_by_other_user.ex

@@ -10,6 +10,8 @@ defmodule Mv.Membership.Member.Validations.EmailNotUsedByOtherUser do
   use Ash.Resource.Validation
   alias Mv.Helpers
 
+  require Logger
+
   @doc """
   Validates email uniqueness across linked Member-User pairs.
 
@@ -64,8 +66,6 @@ defmodule Mv.Membership.Member.Validations.EmailNotUsedByOtherUser do
         {:error, field: :email, message: "is already used by another user", value: email}
 
       {:error, reason} ->
-        require Logger
-
         Logger.warning(
           "Email uniqueness validation query failed for member email '#{email}': #{inspect(reason)}. Allowing operation to proceed (fail-open)."
         )