fix: add deep_dup polyfill alongside blank?/present?

active_support's deep_dup is used in 8 places in the gem (matchers, consumer
interaction builder). Add a minimal Object/Array/Hash implementation to
lib/pact/support/blank.rb so active_support is not required for this either.

Prompted by review feedback from @YOU54F.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 2 people

lib/pact/support/blank.rb

@@ -1,7 +1,9 @@
 # frozen_string_literal: true
 
-# Minimal blank?/present? polyfill for when active_support is not loaded.
-# Skipped entirely if Object already responds to blank? (e.g. active_support is present).
+# Minimal active_support polyfills for blank?/present? and deep_dup.
+# Each block is skipped entirely if the method is already defined
+# (e.g. active_support is loaded by the host application).
+
 unless Object.method_defined?(:blank?)
   class NilClass
     def blank? = true
@@ -38,3 +40,25 @@ def blank? = !self
     def present? = !!self
   end
 end
+
+unless Object.method_defined?(:deep_dup)
+  class Object
+    def deep_dup
+      dup
+    rescue TypeError
+      self
+    end
+  end
+
+  class Array
+    def deep_dup
+      map(&:deep_dup)
+    end
+  end
+
+  class Hash
+    def deep_dup
+      each_with_object({}) { |(k, v), h| h[k.deep_dup] = v.deep_dup }
+    end
+  end
+end