Add Range/ForEach method

[swithek]

It should iterate over all cache items and pass each of them into a func that is provided as a parameter:

func (c *Cache[K, V]) Range(fn func(*Item[K, V]) bool) {
     // ...
}

The bool return value should indicate whether the iteration should continue or be stopped.

[swithek]

And I think it shouldn't extend the expiration time of the active loop item when it's being loaded and passed into the func (i.e., it should work like the Items() method).

[swithek]

It should work like sync.Map's Range and it should be possible to call Set(), etc. methods from within the provided func without any deadlocks.