Implementation of guess_max

[chainsawriot]

In many cases we don't need to go through the entire vector to guess the type, apropos readxl::read_excel(guess_max) and vroom::vroom(guess_max).

It seems that we can implement the same thing here

minty/src/CollectorGuess.cpp

Lines 13 to 29 in 850c046

	bool canParse(
	const cpp11::strings& x, const canParseFun& canParse, LocaleInfo* pLocale) {
	for (const auto & i : x) {
	if (i == NA_STRING) {
	continue;
	}
	if (i.size() == 0) {
	continue;
	}
	if (!canParse(std::string(i), pLocale)) {
	return false;
	}
	}
	return true;
	}

Instead of going through x entirely (for (const auto & i : x)), just go through a subset of the first guess_max items.