refactor: Use is_default_array insead of checking array_length = 0 in noir-protocol-circuits

[sklppy88]

Search TODO: #5618 in the codebase

example:

        assert(
            is_default_array(public_inputs.new_note_hashes), "new_note_hashes must be a default array (zeroed) for static calls"
        );
        assert(
            is_default_array(public_inputs.new_nullifiers), "new_nullifiers must be a default array (zeroed) for static calls"
        );

        let new_l2_to_l1_msgs_length = array_length(public_inputs.new_l2_to_l1_msgs);
        assert(new_l2_to_l1_msgs_length == 0, "new_l2_to_l1_msgs must be empty (length 0) for static calls");