Add padder_type into printer

[kaverdeka]

public:
	template <class PAD_TRAITS, class FUNC>
	struct padder_type
	{
		constexpr explicit padder_type(FUNC& func) noexcept {}
		static constexpr void enable_padding(bool) noexcept { }
		static constexpr void add_padding() noexcept {}
	};

Example:

gtpu::proto proto;
char const* err = gtpu::decode(data, size, proto);
sink s;
med2::print(s, proto, max_depth); // error

Compile error:

../microcore/gate/rfms/src/msg_dump.cpp:217:13: required from here
../microcore/common/codec/med2/encode.hpp:274:47: error: no class template named 'padder_type' in 'class med2::printer<sink_t<100000>&, 128>'
274 | using pad_t = typename ENCODER::template padder_type<pad_traits, ENCODER>;