chore: Formatter can now handle cast expressions (#3000)

Co-authored-by: Tom French <tom@tomfren.ch>

tooling/nargo_fmt/src/visitor/expr.rs

@@ -27,6 +27,9 @@ impl FmtVisitor<'_> {
             ExpressionKind::Prefix(prefix) => {
                 format!("{}{}", prefix.operator, self.format_expr(prefix.rhs))
             }
+            ExpressionKind::Cast(cast) => {
+                format!("{} as {}", self.format_expr(cast.lhs), cast.r#type)
+            }
             ExpressionKind::Infix(infix) => {
                 format!(
                     "{} {} {}",

tooling/nargo_fmt/tests/expected/cast.nr

@@ -0,0 +1,3 @@
+fn main() {
+    x as u8
+}

tooling/nargo_fmt/tests/input/cast.nr

@@ -0,0 +1,4 @@
+fn main() {
+
+x  as  u8
+}