Add helper for PSR-16/void-cache

[SQKo]

A void/null cache class for PSR-16/SimpleCache implementation

might want to have its own repo

[Exanlv]

Suggested change

	$result = [];
	foreach ($keys as $key) {
	$result[$key] = $default;
	}
	return $result;
	return array_fill_keys($keys, $default);

Though not sure if it accepts iterable, so maybe this instead?

Suggested change

	$result = [];
	foreach ($keys as $key) {
	$result[$key] = $default;
	}
	return $result;
	return array_fill_keys(iterator_to_array($keys), $default);

[SQKo]

I thought of this before, but i changed my mind

Now i forgot why i changed my mind, it was probably something with the object's getIterator() implementation and the use of Generator, but not sure which