Fix cursor decoding with only one time column

When the cursor is created with only one time column, decoding it would
crash, reporting that the columns and values have different sizes.

This is because `Array(values)` attempts to call `#to_ary` and `#to_a`
on its arguments before manually wrapping it in an array. This means
that `Time#to_a` is called, which returns an array of 10 elements.

The remedy is to do that manual wrapping ourselves, so that we can
ensure that the values are always wrapped in an array, and then call
`flatten` so that if an array was passed in, it is unwrapped back into
a single level array.

lib/activerecord_cursor_paginate/cursor.rb

@@ -48,8 +48,8 @@ def deserialize_time_if_needed(value)
     attr_reader :columns, :values
 
     def initialize(columns:, values:)
-      @columns = Array(columns)
-      @values = Array(values)
+      @columns = [columns].flatten
+      @values = [values].flatten
 
       raise ArgumentError, "Cursor values can not be nil" if @values.any?(nil)
       raise ArgumentError, ":columns and :values have different sizes" if @columns.size != @values.size

test/paginator_test.rb

@@ -184,6 +184,15 @@ def test_paginating_over_time_column
     assert_equal([7, 4, 10], page2.records.pluck(:id))
   end
 
+  def test_paginating_over_time_column_without_primary_key
+    p = User.cursor_paginate(limit: 3, order: { created_at: :asc }, append_primary_key: false)
+    page1 = p.fetch
+    assert_equal([5, 3, 8], page1.records.pluck(:id))
+
+    page2 = p.fetch
+    assert_equal([7, 4, 10], page2.records.pluck(:id))
+  end
+
   def test_paginating_over_all_pages
     p = User.cursor_paginate(limit: 2)