Use handled Failure for X::Sum::Push::Usage.

  It isn't perfect but at least it gets things up and running for star13
  Still some work to do to adapt to the new sink/failure handling

lib/Sum.pm6

@@ -372,7 +372,9 @@ role Sum::Marshal::Raw {
         # Pass the whole list to the class's add method, unprocessed.
         sink self.add(@addends).grep({$_.WHAT ~~ Failure }).map:
              { return $_ };
-        Failure.new(X::Sum::Push::Usage.new());
+        my $res = Failure.new(X::Sum::Push::Usage.new());
+        $res.defined;
+        $res;
     };
 
     # This allows simultaneous mixin of Sum::Partial
@@ -429,7 +431,9 @@ role Sum::Marshal::Cooked {
                 when Failure { return $_ };
             }
         };
-        Failure.new(X::Sum::Push::Usage.new());
+        my $res = Failure.new(X::Sum::Push::Usage.new());
+        $res.defined;
+        $res;
     }
 }
 

t/sum.t

@@ -175,7 +175,7 @@ class Foo5
         method size () { 64 }
         method finalize (*@addends) {
             self.push(@addends);
-            return fail(X::Sum::Missing.new()) unless self.whole;
+            return Failure.new(X::Sum::Missing.new()) unless self.whole;
             $.accum;
         }
         method Numeric () { self.finalize };