Method error_builder

src/toml.hpp:12925–12931

		char* const max_write_pos = buf + (buf_size - std::size_t{ 1 }); // allow for null terminator

		TOML_NODISCARD_CTOR
		error_builder(std::string_view scope) noexcept
		{
			concatenate(write_pos, max_write_pos, "Error while parsing "sv);
			concatenate(write_pos, max_write_pos, scope);
			concatenate(write_pos, max_write_pos, ": "sv);
		}

		template <typename T>
		void append(const T& arg) noexcept