Remove spree_variants default value and constraint

Some of the production database have default value for `weight` and
`unit_value` has well as check constraint. We want to remove them to
bring the database schema inline with schema.rb

db/migrate/20241211060023_remove_variant_default_value.rb

@@ -0,0 +1,27 @@
+class RemoveVariantDefaultValue < ActiveRecord::Migration[7.0]
+  def up
+    change_table :spree_variants do |t|
+      t.change_null :weight, true
+      t.change_default :weight, nil
+      t.change_null :unit_value, true
+      t.change_default :unit_value, nil
+    end
+    execute <<-SQL
+        ALTER TABLE spree_variants
+          DROP CONSTRAINT IF EXISTS check_unit_value_for_nan;
+        ALTER TABLE spree_variants
+          DROP CONSTRAINT IF EXISTS check_weight_for_nan;
+      SQL
+  end
+
+  def down
+    change_table :spree_variants do |t|
+      t.change_null :weight, false
+      t.change_default :weight, "0.0"
+      t.change_null :unit_value, false
+      t.change_default :unit_value, "1.0"
+      t.check_constraint("unit_value <> 'NaN'::double precision", name: "check_unit_value_for_nan")
+      t.check_constraint("weight <> 'NaN'::numeric", name: "check_weight_for_nan")
+    end
+  end
+end