Cleanup PVF artifact by cache limit and stale time (#4662)

Part of https://github.com/paritytech/polkadot-sdk/issues/4324
We don't change but extend the existing cleanup strategy. 
- We still don't touch artifacts being stale less than 24h
- First time we attempt pruning only when we hit cache limit (10 GB)
- If somehow happened that after we hit 10 GB and least used artifact is
stale less than 24h we don't remove it.

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Co-authored-by: s0me0ne-unkn0wn <48632512+s0me0ne-unkn0wn@users.noreply.github.com>
Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>