Add `Entry#absolute_time?`.

This method returns `true` if an entry has timezone information in its
timestamps, `false` otherwise.

lib/zip/entry.rb

@@ -176,6 +176,11 @@ module Zip
       send(:time=, value, component: :ctime)
     end
 
+    # Does this entry return time fields with accurate timezone information?
+    def absolute_time?
+      @extra.member?('UniversalTime') || @extra.member?('NTFS')
+    end
+
     # Return the compression method for this entry.
     #
     # Returns STORED if the entry is a directory or if the compression

test/entry_test.rb

@@ -340,4 +340,12 @@ class ZipEntryTest < MiniTest::Test
     entry.gather_fileinfo_from_srcpath('test/data/mimetype')
     assert_equal(entry.time, File.stat('test/data/mimetype').mtime)
   end
+
+  def test_absolute_time
+    entry = ::Zip::Entry.new
+    refute(entry.absolute_time?)
+
+    entry.time = Time.now
+    assert(entry.absolute_time?)
+  end
 end