OptCached doesn't take into account the date of the source

[yegor256]

At the moment, OptCached accepts an XML document and returns its optimized version. It also checks, whether an already optimized XML exists in the cache. However, it doesn't pay attention to the date of the original XML and the date of the document in the cache. This often leads to errors because the data in the cache is already expired.

I think, we should change the interface of Optimization from Function<XML, XML> to Function<Path, XML>. It should accept the path of the source document, not the content of it.

Also, I think it's better to use Func from Cactoos instead of Function from JDK, since it allows checked exceptions to be thrown from the apply method.

[yegor256]

@volodya-lombrozo can you please fix this? it's pretty urgent, since it blocks this: #2711

[volodya-lombrozo]

@yegor256 Yes, I'll

[yegor256]

@volodya-lombrozo it doesn't block #2711 anymore, but still would be nice to fix, since the entire caching mechanism is kind of broken now