Implement a LRUCache template class

[pan-apple]

Problem

Need a template class that can be used for caching DNS, CASE Resumption and other similar entries. The following is a list of expected features.

1. Contains a list of cached entries
2. Add/Remove/Lookup entries
3. Configurable maximum size of cache
4. Evict oldest entries from cache if its full and a new entry gets added to it
5. The cache could be persisted in storage, or loaded from storage on specific triggers
6. Unit tests for various use-cases of the cache

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[stale]

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