## Issue Addressed
Closes https://github.com/sigp/lighthouse/issues/2944
## Proposed Changes
Remove snapshots from the cache during sync rather than cloning them. This reduces unnecessary cloning and memory fragmentation during sync.
## Additional Info
This PR relies on the fact that the `block_delay` cache is not populated for blocks from sync. Relying on block delay may have the side effect that a change in `block_delay` calculation could lead to: a) more clones, if block delays are added for syncing blocks or b) less clones, if blocks near the head are erroneously provided without a `block_delay`. Case (a) would be a regression to the current status quo, and (b) is low-risk given we know that the snapshot cache is current susceptible to misses (hence `tree-states`).
efebf712dd