Add support for TTL

[skrtdev]

It would be nice to have caches that expire after a set time

[jeffreyvanhees]

The function is only cached within the current request, so a TTL seems unnecessary.

[skrtdev]

What about long-running processes?

[freekmurze]

People who need that can flush the cache manually: Spatie\Once\Cache::getInstance()->flush();

[skrtdev]

If i could use it it wouldn’t have asked for ttl