chore: remove conditional @impl for new ash_sql callback

Author: stevebrambilla

lib/sql_implementation.ex

@@ -335,11 +335,8 @@ defmodule AshPostgres.SqlImplementation do
     {types, new_returns || returns}
   end
 
-  # Conditionally apply @impl to keep compatibility across ash_sql versions
-  if {:immutable_errors?, 1} in AshSql.Implementation.behaviour_info(:callbacks) do
-    @impl true
-    def immutable_errors?(repo) do
-      repo.immutable_expr_error?()
-    end
+  @impl true
+  def immutable_errors?(repo) do
+    repo.immutable_expr_error?()
   end
 end