$解:(1)\ ①-②,得2x+2y=2,即x+y=1,③$
$③×2023,得2023x+2023y=2023,④$
$④-②,得y=2$
$将y=2代入③,得x=-1$
$所以原方程组的解是\begin{cases}{x=-1}\\{y=2}\end{cases}$
$(2)①-②,得(a-b)x+(a-b)y=a-b$
$即x+y=1,③$
$③×(a+2),得(a+2)x+(a+2)y=a+2,④$
$④-①,得y=2$
$将y=2代入③,得x=-1$
$所以原方程组的解为\begin{cases}{x=-1}\\{y=2}\end{cases}$