Ability to preload the cache at start time

[ithinkicancode]

Motivation

Sometimes it's desired to pre-warm the cache with entries that are known to be frequently used, as an optimization strategy. For instance, an e-commerce web site might want to load the top 100 most popular items right from the start.

Considerations

1. We'll probably need a separate lookup function to retrieve these entries and populate the cache.
2. It's probably a good idea to stagger the provided TTL for each entry so that we can avoid the situation where these hotspot entries all expire at the same time and subsequent requests can trigger an avalanche of retrieval.