Fix RuntimeError when using multiple hash splat operators

When multiple hash splat operators expand hashes of the same type,
duplicate edges were being added to the same vertex, causing `Set#<<`
to raise an error. This can be avoided by using `Vertex#new_vertex`.

Co-Authored-By: Takumi Shotoku <sinsoku.listy@gmail.com>

Author: mame

lib/typeprof/core/graph/box.rb

@@ -380,8 +380,8 @@ def run0(genv, changes)
       @hsh.each_type do |ty|
         ty = ty.base_type(genv)
         if ty.mod == genv.mod_hash
-          changes.add_edge(genv, ty.args[0], @unified_key)
-          changes.add_edge(genv, ty.args[1], @unified_val)
+          changes.add_edge(genv, ty.args[0].new_vertex(genv, :__hash_splat), @unified_key)
+          changes.add_edge(genv, ty.args[1].new_vertex(genv, :__hash_splat), @unified_val)
         else
           "???"
         end

scenario/regressions/hash-with-splat-operator.rb

@@ -0,0 +1,11 @@
+## update
+def opts(prefix)
+  { "#{prefix}_key" => 1 }
+end
+
+def test
+  {
+    **opts(:cat),
+    **opts(:dog)
+  }
+end