[refactor] introduce an LRU cache inside certificate store

[akichidis]

Description

This PR is introducing an LRU cache in the certificate_store in order to minimise the impact from the read operations (only on the primary index at the moment). That will help:

• reduce the number of reads against rocksdb
• avoid deserialisation costs of Certificate

relevant metrics for cache hit/miss have been added.

The cache has been set to hold 100 * 60 items (100 nodes X 60 rounds) - but we can tune further. Also, we only populate the cache when we write a certificate - especially for the cases we are interested I don't consider we need to re-populate on read.

Test Plan

Added unit tests

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Type of Change (Check all that apply)

• user-visible impact
• breaking change for a client SDKs
• breaking change for FNs (FN binary must upgrade)
• breaking change for validators or node operators (must upgrade binaries)
• breaking change for on-chain data layout
• necessitate either a data wipe or data migration

Release notes

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[kchalkias]

In some other uses of LRU we had a wrapper over the lru dependency. Shall we reuse that logic here as a template? ie check this PR
#9056

*maybe @mystenmark and @benr-ml who did that before can provide more intel on this (ie we use this for metrics etc)

[kchalkias]

Check this LRU pattern from @benr-ml as well
#9712

[arun-koshy]

Nice addition Tasos! 🚀

[mwtian]

I think adding a data structures that keeps certificates above GC round consistently should not be much more complex. If we add that in future, do you think we still need the cache?

[akichidis]

I think adding a data structures that keeps certificates above GC round consistently should not be much more complex. If we add that in future, do you think we still need the cache?

@mwtian let's talk more about what you have in mind because for sure I can see other alternatives than this cache. I would still prefer adding this for the time being so we get some gains and we can always remove it later as it's not too invasive. What do you think?