fix: add explicit Block statement (required for scoping)

src/main/wacc/ast.scala

@@ -126,6 +126,8 @@ object ast {
   object If extends ParserBridge3[Expr, Stmt, Stmt, If]
   case class While(cond: Expr, body: Stmt) extends Stmt
   object While extends ParserBridge2[Expr, Stmt, While]
+  case class Block(stmt: Stmt) extends Stmt
+  object Block extends ParserBridge1[Stmt, Block]
   case class SeqStmt(stmt1: Stmt, stmt2: Stmt) extends Stmt
   object SeqStmt extends ParserBridge2[Stmt, Stmt, SeqStmt]