refactor: extract cache logic from getVp

[wa0x6e]

🧿 Current issues / What's wrong ?

The cache engine is tightly coupled to the getVp function, making it harder to test and adding too much unrelated lines unrelated to the core function (almost half of the function's lines are related to cache set and get)

💊 Fixes / Solution

Extract the cache function from the getVp function.

The goal here is:

• to have a more simpler getVp function by removing the cache logic
• instrument the cache engine (in later PR), by tracking how many requests are hitting/missing/skipping the cache
• move the getScores to this cache engine in later PR, to benefit from instrumentation

🚧 Changes

🛠️ Tests

• Current tests are untouched, and pass
• run yarn dev
• run

 curl 'http://localhost:3003/' \                                                              
  -H 'accept: application/json' \
  -H 'content-type: application/json' \
  --data-raw '{"jsonrpc":"2.0","method":"get_vp","params":{"address":"0x91FD2c8d24767db4Ece7069AA27832ffaf8590f3","network":"42161","strategies":[{"name":"erc20-votes","network":"42161","params":{"symbol":"ARB","address":"0x912CE59144191C1204E64559FE8253a0e49E6548","decimals":18}}],"snapshot":143863052,"space":"arbitrumfoundation.eth","delegation":false}}' \
  --compressed

• it should return result with cache: false on first run
• it should return result with cache: true on subsequent run

[ChaituVR]

I have never seen our team using callbacks 🙈 especially less

should that be fine?

[wa0x6e]

It's the most elegant way to do this thing.

We use it in the requestDeduplicator

[codecov]

Codecov Report

Attention: 8 lines in your changes are missing coverage. Please review.

Comparison is base (ddec4db) 72.33% compared to head (037eca7) 75.97%.

Files	Patch %	Lines
src/redis.ts	11.11%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #938      +/-   ##
==========================================
+ Coverage   72.33%   75.97%   +3.64%     
==========================================
  Files          13       14       +1     
  Lines         665      691      +26     
  Branches      106      116      +10     
==========================================
+ Hits          481      525      +44     
+ Misses        180      163      -17     
+ Partials        4        3       -1     

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