Increase speed of Table#to_csv when encoding is provided

If we set the encoding when we call Table#to_csv we do not need
to go row by row to determine the encoding to use. This allows
the use of CSV#generate_lines as a faster exporter.

Author: wishdev

lib/csv/table.rb

@@ -1006,10 +1006,15 @@ def to_csv(write_headers: true, limit: nil, **options)
       limit ||= @table.size
       limit = @table.size + 1 + limit if limit < 0
       limit = 0 if limit < 0
-      @table.first(limit).each do |row|
-        array.push(row.fields.to_csv(**options)) unless row.header_row?
-      end
 
+      if options[:encoding]
+        rows = @table.first(limit).select { |row| !row.header_row? }
+        array.push(CSV.generate_lines(rows, **options))
+      else
+        @table.first(limit).each do |row|
+          array.push(row.fields.to_csv(**options)) unless row.header_row?
+        end
+      end
       array.join("")
     end
     alias_method :to_s, :to_csv

test/csv/test_table.rb

@@ -373,6 +373,15 @@ def test_to_csv_limit_negative_over
     CSV
   end
 
+  def test_to_csv_encoding
+    rows  = [ CSV::Row.new(%w{A}, ["\x00\xac".force_encoding("ASCII-8BIT")]),
+              CSV::Row.new(%w{A}, ["\x00\xac"]) ]
+    table = CSV::Table.new(rows)
+
+    assert_equal('UTF-8', table.to_csv(encoding: 'UTF-8').encoding.to_s)
+    assert_raises(Encoding::CompatibilityError) {table.to_csv}
+  end
+
   def test_append
     # verify that we can chain the call
     assert_equal(@table, @table << [10, 11, 12])