Don't rely on the column SQL type for bit string quoting

Perhaps alias `quote_for_database` to `type_cast_for_database` on base `Value` class. Then in classes which need custom quoting, you can do something like:

```ruby
def quote_for_database(value)
  if binary?
    "B'#{super}'"
  elsif hex?
    "X'#{super}'"
  end
end