Description of your changes

This PR introduces a Least Recently Used (LRU) cache to the BasePersistenceLayer of the upcoming Idempotency utility. In this type of cache the most recently-used items are kept in the cache while older ones, that have been accessed less recently are evicted as new items come in.

Users can configure any persistence layer that extends the BasePersistenceLayer to use this cache, and in doing so they can also specify the maximum amount of items that are kept in the cache:

const persistenceLayer = new MyPersistenceLayer(); // i.e. DynamoDB
persistenceLayer.configure({
  config: new IdempotencyConfig({
    useLocalCache: true, // defaults to `false`
    maxLocalCacheSize: 50, // defaults to `256`
  }),
});

When caching is enabled, the persistence layer stores, retrieves, and deletes idempotency records from the cache.

Notes on the LRUCache implementation

As discussed in the linked issue, contrary to Python, Node.js doesn't have any LRU Cache implementation in its standard library. Prior to working the PR I have researched popular modules and found two: lru-cache (123M weekly downloads) and lru_map (3.7M weekly downloads).

While both libraries are popular, the lru-cache one offers a wide range of features like TTL, retrieval functions from remote, and a host of other features that we weren't going to be using in this utility. This, in addition to the module size (638 kB unpacked - vs ~150 kB on average on our side), made me opt for the less popular one.

When looking at the lru_map module, I realized that the recommended usage stated this:

Recommended: Copy the code in lru.js or copy the lru.js and lru.d.ts files into your source directory. For minimal functionality, you only need the lines up until the comment that says "Following code is optional".

For this reason I have opted for reimplementing the module directly in our repo. The resulting implementation follows loosely the one found in the lru_map module in terms of flow, but adds type annotations, comments, unit tests and retains only the bare minimum methods/features that are needed for Idempotency to work.

The result of this work can be found at packages/idempotency/src/persistence/LRUCache.ts and the license as well as a direct mention to the original implementation and recommended usage are included in the docstring of the class.

For now I have opted for putting the class in the Idempotency utility, however in the future we might consider extracting it in the commons package so that it can be used by other modules, as well as customers in their own code.

Once merged this PR closes #1299

Related issues, RFCs

Issue number: #1299

Checklist

• My changes meet the tenets criteria
• I have performed a self-review of my own code
• I have commented my code where necessary, particularly in areas that should be flagged with a TODO, or hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding changes to the examples
• My changes generate no new warnings
• The code coverage hasn't decreased
• I have added tests that prove my change is effective and works
• New and existing unit tests pass locally and in Github Actions
• Any dependent changes have been merged and published
• The PR title follows the conventional commit semantics

Breaking change checklist

Is it a breaking change?: NO

• I have documented the migration process
• I have added, implemented necessary warnings (if it can live side by side)

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